To me it seems that just declaring them unspendable is the option that changes incentives/rules the least. Giving the coins to miners changes the rules.
Imagine that this situation happened when 99% of the coins were mined and suddenly 10% of coins were going to be given to miners, giving them 10x as much as before this decision.
Doesn't make much sense to me.
Edit: The change that does the least change in incentives is to announce that there will be a window of spendability that reaches X years back at all times, where X > the oldest coin. Then no coin is invalidated now, but a rule that keep uncertainty bounded has been introduced.
Why exactly do you feel it's so wrong to change the incentives in this fashion? If recycling was added now with a 100 year shelf-life on coins, there would be PLENTY of time to account for the added mining incentive coming way down the road. I know some are concerned that transactions fees won't be enough incentive to secure the network down the road and this would add to the incentive without increasing the intended supply of coins. Again, I no longer think this is needed but like to play devil's advocate...
Some how, some way, we need to teach every noob how to use the search function. Maybe they should all have to prove they know how to search for a topic before they get out of noob jail? Moderators, can we make this happen? Just some sort of test where they have to use the search function once before they are allowed to post "new" topics?
This is wishful thinking. If you really want to solve this problem, require that anyone who wants posting privileges post a bond, in Bitcoins. Some nominal fee like $25 worth of Bitcoins. If they break the forum rules, like posting something that could have been found via search, they forfeit the bond. Problem solved.
Solve what problem? The problem of bitter vets having to scroll past a topic they've already discussed? I have a solution that's much easier. Just ignore posts that you are not interested in participating in. You could also just link to the previous topic which would take just slightly longer than posting a complaint. Or you could contribute and help educate the new generation of bitcoin enthusiasts.