Re: older still legal Shure wireless
Wireless technology is something that is moving and advancing extremely quickly. While generally speaking, the older high end stuff is probably more robust than new cheap solutions, the fact is, the gap has narrowed quite a bit.
The downsides of older gear are sound quality (compared to new of the same class) and frequency agility. New systems can cover a HUGE range of frequencies that allow you to be far more flexible in frequency selection. The sound quality of higher end systems is going to be better than cheap gear, but even today's entry level digital systems offer amazing quality that can equal or surpass the high end gear from yesteryear.
An additional thing to concern yourself with is the availability of replacement pieces when you need them. If your old wireless dies and you need a replacement that fits into your system tomorrow, can you do that with an old discontinued piece? Current products can generally be overnight delivered from many suppliers.
If the price is extremely lean and you can get a spare unit or two, then older gear might be a good idea. If the savings isn't that great over a comparable new product, then I'd shy away from it.