Rutan,
No I don't think so. I've been building and tuning engines (and modifying the advance curves of Lucas distributors) for well over 40 years. My bedside bookshelf is full of engine tuning manuals from a whole range of authors. I also used to teach piston engine theory to RAF student pilots. I've never seen any evidence that a less than optimum ignition timing setting causes valve seat wear. If ignition timing were drastically incorrect, i.e. too far advanced, detonation would be the immediate result. If too little advance, the result is less than optimum engine performance. Generally speaking, a higher octane fuel can tolerate a more advanced ignition setting.
On the other hand there is a great deal of evidence that the removal of TEL from petrol for environmental reasons resulted in rapid valve seat recession on many older engines. Many of them had to be retro-fitted with good quality, hardened steel valve seats (as did my old design motorcycle engine a few months ago). LPG obviously contains no TEL.
AVGAS contains a relatively large amount of TEL, even the advertised "Low Lead" (LL) quality (a reduced amount compared to that from years gone by, but still about five times the amount that the old 4 star road fuel had). Some years ago I experimented with an unleaded / LL AVGAS mix in a very high compression competition engine I had built (it was quite common to do this). I researched this and was surprised to learn that I only needed about 1 gallon in 5 of unleaded to bring the octane rating up to the desired level. The engine loved it. What surprised me was that the colour of the inside of the tail pipe went from black to grey with just one tankful, as did the plug colour, just as in the old days of "proper" leaded fuel.
LPG naturally has a very good octane rating but is known to cause valve problems on some engines (see the list in the link below) because it is generally seen as a "dry" fuel. I have a brand, old stock Lucas distributor originally intended for an LPG engine (Land Rover) in my garage. I used to collect new old stock to dismantle them for parts or just use the bodies to build on. I stripped it down but I soon discovered that it has considerably more total advance (taking into account both mechanical and vacuum) than those required for any petrol engine I've come across.
Valve Seat Recession Explained
Here's another interesting link:
LPG Problems