If you have paid for your dining plan then you do want to try and get the best out of it, which to many means at the very least, a break-even with what you have paid. Remember when calculating prices that your dining plan includes tax at 6.5%. The menu prices do not. And with Disney's rate of inflation it is pretty easy on the regular
DDP to justify the expense of the plan. However there is a happy medium between working at trying to get the maximum value out of the plan and actually letting it work for you. To me, trying to order the most costly things off the menu defeats the whole purpose of the 'convenience' aspect of adding it in the first place as it then just becomes a bit of a chore. If you feel like ordering a chicken salad and feel you need to go for a steak just to get value for money I think you've lost half the battle already. Just my take on it however.
As above, you will get better value on dinners. However that should not stop you from enjoying some breakfasts and lunches if you prefer and if they suit your touring plans better for the day. A little bit of everything should still bring you out well ahead in terms of cost.
As far as the approach to 'wasting snacks' on things like bottled water, I am in the minority with my take on it. Yes, a bottle of water is not a good use of a snack credit
IF you are going to use all or nearly all of your snack credits during your stay. However saving up snacks and paying out of pocket for waters and sodas so as not to 'waste' credits, only to end up on your last day running around trying to redeem leftover credits for snacks makes little economic sense to me.
There is a sticky on the Dining Plan sub forum. It is kept updated on a regular basis and everything as reported by guests on their return as an eligible snack is added to the list, which is categorised by location to make it easier to reference. What I do notice on here is that the snacks are being updated, but the prices are not as the items we ordered in October which are on that list were already then at least 10-20% more expensive and tax still needs to be factored in. From what I can work out, most of the items reflect 2009 prices, but it will give you a general idea. Here is the sticky:
http://www.disboards.com/showthread.php?t=2640292
For counter service, here are some of the winners in terms of value (if you care for the items listed of course):
Personal favourites:
Main Street Bakery Cinnamon Rolls
http://www.disneyfoodblog.com/2010/05/14/disney-cinnamon-roll/
Aloha Isle in Adventureland: Dole Whip Pineapple floats
The Lunching Pad in Tomorrowland: Frozen Cherry Eclipse
Epcot cart near to the Land Pavillion: Cinnamon Pretzels - hot and yummy!
(Excuse us, but we started eating it before we remembered to take a picture

)
MAGIC KINGDOM
Cosmic Rays: Rib & Chicken Combo - $14.19 plus tax
Pecos Bills: Angus cheese burger - $9.09 plus tax
EPCOT:
Sunshine Seasons (love this place!): Seared Tuna Noodle Salad - $9.99 plus tax
Asian hot meals - all $9.99 plus tax
SS has an amazing selection of desserts to go with your food too
Tangierine Cafe: Chicken & Lamb Combo Shwarma platter - $13.99 plus tax
ANIMAL KINGDOM:
Flame Tree BBQ: Half rack of ribs - $10.49
Half grilled chicken - $9.49 plus tax
Yak & Yeti Counter Service (it's called Andapur Local Food Cafe): All their hot meals come in at $10 before tax and I really like the food here - its something different too and not the usual CS fare you find in most of the Disney QS locations
HOLLYWOOD STUDIOS
I am not crazy about CS here, but Starrin Rolls have some really good offerings but you need to get there early as they close when they sell out which is usually round early to mid afternoon, depending on the time of year.
They serve Deluxe focaccias which are HUGE. You also get the usual choice of beverage with it as well as your choice of any of the decadent desserts in the case and also a whole fruit or a bag of chips (crisps), which makes it pretty good value. DD and I got the latter and it totalled around $17 for that meal and was one CS credit.
DOWNTOWN DISNEY
There is no contest on this one: Wolfgang Puck Express
You can easily rack up a bill averaging $20 -25 per person if you get a full main meal and your beverage and dessert. The food is really good and it is pretty much a table service meal for a counter service credit. Be prepared to leave a tip though as you are served, but honestly, it is so worth it.