I used to give them a very quick wipe with thinners. Gives a really great matt finish and evaporates almost immediately.
Re the silicone I'd check the tyre manufacturers sites to see if they warn against any chemical use. As I say I think the tyre bling industry is mostly marketing.
S
If you're not living on the edge you're wasting too much space!
I decided to go and get some expert advice on the 'Does silicone damage tyres?'. Fortunately I didn't have to try too hard as my better half is a process engineer at a company that makes rubber for car tyres. The response was that silicone forms part of the compound used in the manufacturer of the tyre so its very unlikely to have any damaging effect. So Stephen is correct, all marketing.
I'm pretty sure spewing on them won't help either the condition of the tyre nor cause any degradation. Can't talk for pee on the front near side neither.