What kind of bitcoins goes on those 'Casascius coins'. The ones you use to purchase them or something else because it'd be good if you could get whole virgin BTC25.00 blocks on them 
Usually it's just the one used to purchase them, but I would be happy to make 25 BTC coins out of virgin coins if there were buyers willing to pay extra to make the effort worthwhile. Part of the problem is that everyone agrees they'd be neat but wouldn't pay much more than a couple percent premium to get one. I'm open to be proven wrong, but am somewhat resigned to the idea that bothering would barely be worth the effort.
If someone wants to arrange it themselves, I'd be very open to it... in other words, you buy the coin and then instead of saying "OK it arrived please fund it", you'd say "OK it arrived and I funded it myself so you don't have to, so now please refund me my original 25 BTC at address X". I already do deals very similar to this from time to time when buyers want to fund them with bitcoins from a specific origin.
I could see Virgin Casascius coins as quite interesting because they bring a physicality to the idea of a pure block. I could see down the road people being interested in such a coin being more collectible than others. The difficult part is how such an item could be traded if the private key is not trusted to be destroyed. I come back to the same as your other coins - perhaps the trust of Casascius destroying the key is better than the trust of the first buyer doing so?
People have always collected things and when those things are rare things the collection can become valuable. Certain gold coins coins are worth >x10 the magnitude of 'spot' price.
