I'll be living in Kunming with roughly 75 dollars a week for food and day to day expenses. Does this amount sound adequate for living, what you would consider, a decent lifestyle?

American dollars that is.

Well, depends on how you want to eat really!

A local meal cost between 5-12 RMB for a plate of food. It would cost around the same (or a little bit more) to cook for yourself using local ingredients from the market/supermarket. Average western meal would cost around 25-50 RMB for the same. So you should have some idea about how much food costs here.

Entertainment (going to pubs/clubs etc)... well it depends how much you want! A new theatre costs 120 RMB is the most expensive I have seen here, 40 RMB for a lower quality theatre. Beer costs between 12-18 RMB for a local beer (Dali, Tsingtao or Budweiser, strangely enough!) or around 20-60 RMB for imported beer from europe or Australia. Karaoke costs around 120 RMB plus beer/snacks on top of this, if you are into that sort of thing!

I am easily living on 2000 RMB per month (75 USD approx 500 RMB, multiply by 4 = 2000 RMB per month) eating the occasional western meal, NOT including rent (1000 RMB per month for a nice place) or power and with a couple of nights out per month. I think you should be fine on that budget as long as you don't want to live it up.

Blobbes answer is about right, but one correction. Local meal is 5-25 yuan, not 5-12, excluding beverage.

Part of town is important. I have had a proper meal with 3 dishes- delicious, nutritious and big- for 6 yuan, and the same meal in a more posh area for 30. Also depends on how big you are, how active you are, how much meat you prefer, if the restaurant is a chain, if it is a known name, if they have waiters/waitresses, etc.

Good luck.

Lemme see...
$ 75 = ¥ 500

Wow. You speak only of food and day-to-day expenses, that means it doesn't include lodging or any other biggies like study fees. So just food, drinks, sometimes a night out with friends, taxi and bus fees (they're really cheap here!), money for things you might need to buy (whatever these may be)...
Sounds like you'll be lucky.

I'm here on a scholarship (no study fees, no lodging costs), getting ¥ 1400 ($ 212) a month, which equals ¥ 350 or about $ 50 a week. Somewhat less then you. I'm curious and I love statistic, so I kept accounts for the half year that I'm here, only couting daily expenses, excluding bigger expenses like buying a digital camera, a smartphone but including a two-week travel to Thailand.

They were quite high in the first weeks, but then got considerably lower. For a student with a scholarship, ¥ 1400 a month is really well calculated (my monthly expenses are sometimes above, sometimes below that value). But then again, I don't smoke nor drink, don't need expensive things and I avoid going to places like "Foreigner Street" too often (really, there's way better and cheaper food in other places).
I think, if you don't go out to party every night or smoke excessively, $ 75 a week will be quite much. It's easy to spend all the money, but once you get used to China, you can live with much less and still have a decent life-style.