Mining is complex business.
There's electricity and heat costs, and even though you say you're not running it for a profit these costs can lead to a substantial loss(depending on where said person lives) which doesn't make it worthwhile.
Also having just one miner won't give you any substantial hashrate so I fail to see the point of buying one in the first place.
If the total hashrate of the network was low enough that having just one miner would give you a decent shot at finding a block then it would be a good idea, otherwise it's pointless, really.
Running a bunch of low hashrate miners doesn't give you a shot at finding a block so it doesn't make mining "more decentralised"
Ditto with forming or joining a pool, if the pool gets big enough it leads to the same problems you're trying to solve.
We wouldn't have the high fee stuck on the blockchain of unconfirmed transactions.
Increasing hashrate does nothing to unconfirmed transactions.
Unconfirmed transactions are as a result of the bitcoin block size (now block weight)
There will always be an average of 1 block every 10 minutes no matter the hashrate -- even if we could harness the full energy of the sun.
If you want lower fees then use segwit and tell others to use it also.