Short answer: Yes.
Longer answer:
The value of a ssd is the very low latency for random reads and writes. That is what the os does most of the time. It will be 50x faster than the fastest hard drive. Random reads are not much dependent on transfer rates, so sata 2/3 is not important.
For sequential operations, sata 3 is faster. sata2 will be 2x faster than a hard drive, sata 3 will be 3x faster. Regardless of which type sata you have, a ssd is a very good performance enhancer.
You will not regret buying one.
And... larger ssd's perform a bit better. There are more nand chips that can be read in parallel.
I suggest a 240gb ssd if you can.