Money is a personal choice. $140 is a good deal. I think $400 for Thiels is an equally good deal...possibly better if quality of sound matters that much to you.
I think what you will find with the Thiels is a few things:
1. They will continue to improve as your electronics improve...beyond the Snells.
2. In particular, the linearity, extension, dynamic range, probably bass performance will all have very strong technical capbilities that should exceed the Snell. You should find that the quality, clarity, extension up and down the spectrum, soundstaging, and detailing are all superior. the speaker should also deliver significantly more punch when you drive real high current thru it...and Thiels can (and should ideally) get a high-current amp to run them. SS Class A amps (the old Forte 4 was a winner of a 50 watt/channel Class Amp!)...will do great here.
3. The key, with any speakers, but particularly in this case...is ensuring you are showing them off to their potential.
If you are going to use very rudimentary electronics, you may yet find you prefer the Thiel...but if you use good quality electronics...i think you will find that Thiels capabilities continue to rise to the occasion comfortably beyond where the Snells start to lose ground.
good luck and hope that's somewhat helpful as one person's opinion.