This will not fix the broken Hamlets, sorry to say.
Most people avoid hamlets period. Only the noobs and coiners play Hammies.
Why?
1. The "harvesting" time is WAY WAY WAY too slow. You get much too little back for the troops you will have to sacrifice.
2. You try go get a few sapphs or metals for Mareth, but then you get obliterated by a big dude before you get there (unless you sacrifice all your troops)
3. You smack someone's hammy TOO big or "possessive", they go take it out on your castle. Or league for that matter.
But still. Point 1 is the crux.
Rest of Hamlets is broken beyond repair. There is hardly any point to Hamlets considering what you WILL lose.
'Players are avoiding hamlets held by players above lvl 100'. See absolutely no evidence of this whatsoever. Correct statement would be players avoid hamlets completely - whenever I look there are zero players on hamlet, absolutely all empty.
So suggestion is trying to fix a problem that doesn;t exist or at least isn't the problem with hamlets at all.
But even if that wasn't so, don't we think the game is unbalanced enough as it is. Giving mega coiners shop only items that whose purpose is to lull average or normal players to their death can't ever be good for the game.
Besides has level fo anything to do with hamlets, when a lvl 50 could have an entire major league supporting it?
So in summary, not addressing the real issues. Shop only items not the right direction for the game. And wouldn't achieve what the OP wants anyway given lvl is kind of irrelevant now hamlets are not 1 v 1 affairs.