OK so the SSD is in the memory is in, OSX is freshly installed on the new drive and I'm off and running.
Holy moly, it is a totally different machine now. The install took forever for some reason but now that I'm in, the machine is so much more drastically responsive. Amazing improvement.
I failed to do a speed test before I pulled the old drive. I suppose I can install that utility and run it and share it once I've done that. I'm in the midst of installing apps and downloading crap from the cloud and my 50,000-message inbox into outlook so I can't get a true result until later once this machine has had time to settle.
Interesting note, TRIM seems not wanting to enable no matter what I do. The built-in command takes, it reboots as expected but trim support still says no under system information no matter what I do. SanDisk states that it doesn't matter, that the controller on the SSD will automatically handle garbage collection and deal with blocks when the drive is not in use. It apparently should be enough to address the issue on a drive for my usage pattern, which is fairly light with a lot of idle time. In a heavily-abused machine dealing with lots and lots of writes and deletes, it might be an issue. Whatever. Aside from the apps and OS, I'm never going to fill up this drive and if I do notice any degradation, I'll just attach the old external HD, clone OSX to it, nuke the SSD, format it, and copy the clone back. I can handle doing that once a year.
In the meantime, the performance increase so far is awesome and I highly recommend anyone willing to crack open an older macbook consider it. I see no reason to push to replacing this machine anytime soon, now.
Now that I've got more memory and the SSD in here, the only thing I can foresee becoming a problem is the battery. I'm at half the number of cycles before it is technically considered exhausted, though the system reports it as healthy. The good news is that genuine Apple battery replacements are easy to come by at about $100 and I have all the tools already.
Note: be sure to have the right screwdrivers for the SSD swap. Those torx screws to hold the drive into the caddy will be a nightmare if you don't have the right piece. Bite the bullet and order it.