If your machine has enough memory, you should not see that much difference with ProE performance on a ssd or standard sata.
I just run OCUS benchmark on a Win 7 64 bit system with 4 gb, then the same tests with 12 GB and standard sata, then the same tests with the 12GB and SSD and there is very little difference in the 12 gb results, the ssd actually looked slower on some results, but that could just be where the wind was blowing : -)
So put your working files where its easy for you to administer. We keep all user info, cache etc in a "Users" folder under the ptc install folder. the Creo Agent always puts stuff in App Data\Roaming and Local as well
Don't know if there are any performance increases with Mechanica, will get one of my guys to test this and see if we get any speed increase splitting the results to data
I now run Mechanica on a RAM disk (24 GB machine; Pro/M WF4 can only use 8 GB). There are definitely speed increases both from putting the temporary files on a fast 'disk', and from putting the results there. For large analyses, the results are written non-sequentially across maybe 12 files so you could see a big improvement from writing them to an SSD.
I don't know what the cost is likely to be in terms of 'using up' disk write cycles... but the best thing is probably for you to experiment using your typical analyses, looking at all three combinations of temp files, results, and both on the SSD.
Below are some results of my informal SSD testing in my HP 8740W laptop.
Launch Pro/E (WF5)
Start up windows 7
Launch Solidworks 2010
OCUS HD test
Reading from SSD has a huge improvement, write is about a wash or can be slower in some cases. If you data is on your SSD when you load it, it will be quicker, saves will be a wash.
Make sure you have the SSD firmware up to date and any windows/bios settings set properly. I have a crucial drive that needed power to the drive during sleep mode so it can do maintenance. I didn't have this set so my drive filled with "garbage". In the sleep mode, it will go through and clean the garbage (this keeps the drive from witting to the same spot over and over from my understanding). My drive filled with garbage and would not boot. I had to reformat and update firmware to bring it back to life. Just a PSA.