Whether it's worth it depends on a few things.
What kind of AP hotel discount can you get? You can actually call Disney reservations and ask for the AP rates for your dates even without actually having an AP yet. Once you know the rates for the dates and room type you are interested in versus non-AP rates that are available, you will know how much savings you will get on the room. Standard AP hotel discount is 10%, but there are better rates offered periodically. I know I recently got an e-mail with better discount rates and Hydroguy posted a thread about that too. Don't know the rates though for your particular dates.
Are you returning to the parks within one year? If you get a second trip out of an AP, that can make it worth it right there. Doesn't sound like this is the case for you.
Do you plan on being very spendy? Our family doesn't spend enough in one trip to make an AP worth it for just the dining and merchandise discounts alone, but we go lots of times during the year so that's the value to us (and during those lots of times we "save" a bundle with the discounts too).
Here are some numbers to consider:
Deluxe AP = $329
Premium AP = $459
If you are going during July 4, then blockout days will most certainly apply if you get the Deluxe pass. Blockout day tickets cost $50 each.
Deluxe has 10% discount at most food places in the parks and hotels, exceptions seem to primarily be locations defined as "snack" locations such as the Mint Julep bar, popcorn, churro, ice cream carts, and ice cream shops. Deluxe also receives a 10% discount on most park merchandise through the end of this calendar year. This does include photopass pictures/CDs, candy shop purchases, ride photos, and purchases at most of the in-park stores and World of Disney and D-Street in DtD. It does not include the silhouettes done at the silhouette studio, the crystal shops, and a couple other places. Deluxe passholders also get various discounts in DtD, most often 10% off.
Premium has 15% discount at the food places in the parks and 20% discount on the merchandise with the same restrictions as noted above. The DtD discounts are the same regardless of pass type.
That means to break even on the purchase of a Deluxe pass, you need to spend $1680 in the parks and in downtown Disney on food and merchandise. The need-to-spend amount increases if you have to purchase one or more block out day passes. The day you purchase your Deluxe pass you can enter the parks even if it should be a blockout day, so if only your first day is a blockout day you will be ok.
To break even on the purchase of a Premium pass, you need to spend between $1240 and $1653 in the parks and in downtown Disney on food and merchandise (I've left the lesser discounted places in DtD out of this equation for simplicity). The $1240 represents merchandise spending only. The $1653 represents food spending only. You will spend on a combination of these items, hence the "break-even" range in this case since food and merchandise have different % off discounts.