Also, is there actually any difference between a 2.4 GHz 2008 MBP and a 2.4 GHz 2010 13" MBP? Besides faster RAM, is anything else different?
Yes, there are a few differences that have been missed.
The 2008MPB has FW 400 as well as FW 800, it has the Expresscard/34, it has DVI out, different keyboard (i think it's better), it has dedicated video memory, and it has better screen resolution (glossy was optional back then, not standard).
On the other hand the MBP 13inch is expandable to 8gigs of ram, the mini displayport is said to be able to pass through audio, the glass trackpad rocks, and the unibody design is a heck of a lot more rugged than the early 2008 MBP.
My opinion:
I had the early 2008 MBP with the 8600 and it did fail. In fact, it failed twice and the second time Apple upgraded me to the new (at that time) unibody MBP.
I am pretty sure i got lucky when they gave me a new MBP Unibody when my MBP 8600 died. Having said that i'm not convinced that if your 8600 does die that you won't get jerked around. Nothing against Apple, I just think there is too much variation in the quality of service. Too much seems to depend on the technician you get, their mood and the store manager. Having said that, I know I am more risk averse and would start looking for a solution before I am forced to find one.
My solution to your situation would be:
If i were you and you couldn't afford a new 15inch MPB:
I would look for a late 2008 unibody at roughly the same price point (or less) as a new 13inch MBP.
This is why i would look for a late 2008 MBP over a new 13inch MBP.
1) Expresscard/34 (great for esata cards)
2) The 9600/9400 (which is still better than the 320 found in the 13 MBP).
3) Better Screen resolution
4) Bigger Screen (better for photos and games)
5) Dedicated Video Memory
The major down side of this strategy is that you would be buying a used computer and the ram is limited to 6 gigs rather than 8 gigs.
Does this help? I hope it doesn't just muddy the water.
~ Curt