Last fall I upgraded my Early 2009 UB 17" with a Crucial M4 512GB SSD ($379). Even though the MBP only had SATA II, I went with something with enough performance left for even SATA III - a bit of future-Mac proofing, if you will. Since it's SATA III, it'll make a newer Mac happy, or at least, a great USB 3.0 external. As it ended up in my case, it allowed me to offer the new owner a great deal to leave the SSD installed when I prepped it for him. (Sold the MBP for my 15" rMBP Mid-2012 loaded w/ all internal options installed - see sig.)
Anyway, the drive it replaced was a Seagate XT, which was nice, but no SSD. After the SSD was installed, I wouldn't say it was a night/day difference, but the system as a whole felt like a new machine. Boot times definitely were much faster, as one would expect. I don't restart much, so I didn't have much good start times to compare off of. I'm sure others have a bit better data on that point than I do.
I think an upgrade to 8GB of RAM is a no-brainer these days $61 for PNY 8GB kit (2x 4GB) at Amazon, or around $73 for Crucial or Corsair. I did this upgrade at the end of 2009 for $77 (the Crucial 8GB kit PC3-8500 (2x 4GB SODIMM)).
Bottom line? Well, for ~16% of the price of a new rMBP (I used $2800 for a 2013 15" 16/512) you'll get a machine that'll respond more like one from a couple years ago, at least to where storage is a bottle neck. Extra RAM will help if you keep lots of things open and or are editing large files with many effects. The more it can keep in physical memory, the better.
So, if you're not ready to just jump into a new machine for whatever reason, I think you'll get at least a couple years more life, most likely still be able to run the latest OS, and be able to watch what'll be new on the horizon. The only reason I sold mine so quick after installing the SSD is that one of those "deals you can't refuse" came along. I really
was planning on keeping the 17" UB until at least this fall to see what'll be out. Really!
