Recondition my 1986 Thiel CS1.0 or buy new?

Thiels have come a long way, mainly for the better. If you can compare yours to newer ones, you might find that its well worth selling your 1.0's and putting that plus the $400 towards a newer model. Your amps will appreciate the easier to drive load as well.

Take the store up on the in-home demo. That is the only way you will know for sure. I had to sign up for an in home demo at 1 local store and the salesman suggested picking it up on a Saturday. The store is closed Sun and Mon. Another option would be to bring your speakers to the store but the chances they have the same electronics and room configuration is pretty nil which again you should take them up on the offer.
Good Luck

Elevick, while perhaps not as sensitive as some of Thiels newer models, I think the the impedance load of the Thiel CS 1 is lot easier on amplifiers than the newer Thiels.
Raya, if they're not broken, I'd leave them alone. Though perhaps undervalued on the used market, they're probably not worth $400 on the used market, so the repairs/ shipping appears to be a poor value. They're still good speakers, and I'd caution one against assuming some newer speakers sounding different as actually being better. As much as you might trust your dealer, at this price point, and considering the value of the dollar today as compared to your 20+ year old then costing $1000 Thiels, I don't think the technology has improved that much. I'd imagine you'd be getting a lot less for your 2011 $400 with a new speaker.

I am going to take the store up on the in-home demo. If the sound is only slightly better, I'll stay where I'm at, If it blows me away, then I have a decision to make.

That seems like the best course of action. Let us know how it goes.