I'll give you my long story/opinion:
DH & I got married in 1991 & went to WDW for our honeymoon. We stayed at the Beach Club Hotel. Driving around WDW one day, we saw OKW being built. I said "We should look into that" since we had already decided that WDW was going to be a place that we were going to be going on a pretty regular basis. DH, the realtor, thought that perhaps we should save for & buy a house before we bought a vacation timeshare...Mr. Logical.

So that's what we did. We spent the next few years going to WDW 1 or 2 times/year, staying in moderates for the most part, with an occasional foray back to the Beach Club or over to the Swan/Dolphin. We bought a house in 1994 & bought our first DVC contract (200 points @ OKW) in 1997. I will tell you that my DH the realtor looked at this purchase every which way from Sunday and determined that there was no way we would probably get hurt financially. We took out the 10 year loan, since that had the lowest monthly payment requirement...we figured that all we HAD to pay was the low payment, but we could always add more to it to pay it off more quickly. One thing we did quickly determine was that we would get the best return on our investment once the initial loan was paid off. So that's what we did....every month we would pay more toward the loan, and we got that 10 year loan paid off in about 3.5-4 years...it's been awhile now so I don't remember the specific time frame, but I know it was paid off by 2001. There were those who were of the opinion that we could have taken the $$ spent on DVC & invested it and gotten a better financial return on our investment, and they are probably correct. However, our train of thought was "This isn't a bad choice for us, we like Disney, we like going, we like being able to bring people with us, and if we are going to be coming here yearly anyway, why not be able to have bigger, better accomodations than just a regular hotel room?".
The caveat here is that the cost of the DVC fit into our budget without causing any financial hardship whatsoever. I will say in no uncertain terms that, no matter how much we both love WDW, we would
not have purchased DVC if it meant that something else was going to suffer. We were still able to save for retirement, we were still able to easily pay all our other bills, we were still able to do all the things we had been doing. Adding DVC wasn't a "stretch" for us.
So 2001, comes, DH's parents both get sick and die

, DH gets left some money. We put osme of the money into home renovations, we put osme of the money into retirement accounts, we buy another 230 point DVC contract with some of the money!!!

So, we currently have a total of 430 points, which allows us to stay for our whole vacation in a DVC property, instead of having to spend a couple of days in a moderate hotel (to conserve points) and then move to the DVC property.

So it has given us more freedom and flexibility.
So basically what it boils down to is this...now that my DVCs are fully paid off, the only charges I have are the monthly maintenance fees, which amount to about $2000/year. For this $2000, so far I have spent 10 days in a 3 BR GV at OKW in January and will shortly be in a 2BR villa at OKW for 6 days in July. So, my deluxe-level accomodations for this year thus far have cost me $125/night...not bad....
When we were intially looking, DH determined that if we went to WDW either yearly or every other year, that it would still be a good investment. If you plan on going every other year, one year's points can be banked and used the next year. So for example, if you have a 150 point contract, that means that every other year you would have 300 points available for your use. You can do pretty well at a DVC with 300 points.
Some things to think about:
~Do you like planning vacations pretty far in advance? While we have sometimes been able to "sneak in" at the last minute, it really is better if you are able to do advance planning.
~Buy where you want to stay. Yes, they will tell you that you can stay anywhere with your points, and you can,
depending on availability. If your vacation will be
ruined if you cannot stay at the Beach Club, then make your home resort the Beach Club because it gives you the 11 month booking window, so you'll have a better chance of actually being able to stay at the Beach Club. When DH & I bought, OKW & BWV were the only 2 properties available. OKW was a bit cheaper per point, we looked at them both, we liked them both, we bought OKW. What we asked ourselves was "If we could never stay anywhere else on WDW property except for here at OKW, could we be happy?". The answer was yes, so that's where we bought. We have been fortunate because since we don't have kids, we travel at "off" times, so we haven't had much issue with getting in where we want, but the possibilty always exists that at any given time, there will only be availability to you in your home resort.
~Your best use of points is staying at a DVC resort. Yes, you can switch out with their sister timeshares, and go on cruises and even use points to stay at the Poly or the Carribbean Beach or some other non-DVC resort, but you will burn through points quickly that way. So, if you're buying DVC to be able to go on all sorts of other trips outside of the DVC resorts, just be aware that you go through points faster that way.
~You are buying a vacation experience. If you are truly a person who is happy staying in a cheapie motel because you literally spend from 6Am-midnight schlepping through the parks, you may not need DVC. I have noticed since buying DVC that our WDW vacations have a bit more of a relaxed pace. We tend to linger in the room a bit in the morning, we make a light breakfast (cereal, toast, fruit...we do not do any significant cooking on vacation...light breakfast and snacks mostly), we relax on the deck and look at the scenery. We go often enough now where if there is an attraction that is crowded, we feel no need to wait in the 2 hour line because "we'll see it next time". Sometimes we go to a park, don't ride a thing and just walk around soaking up the ambiance...the World Showcase in Epcot is one of our favorite places to do this. DVC and our ability to go more often because of it has afforded us this luxury. But, if you truly are the run, run, run type on a Disney vacation and don't see that changing, you may not need that extra bit of vacation luxury and, especially with some of the current discount offerss, you may do better staying in regular hotels. That really is something to consider.
So, think about it, long and hard. Think about your finances, think about what you want from vacation, think about how you vacation. We have never regretted our purchase, but DVC is not for everyone.