So much of what we chase in tone is subjective to our own ears. So in essence this can’t be answered. If it sounds better to you insulated then so be it. If not then don’t. I think that applies to everything in guitar though. Just my 2 copper.
That gives you more separation to your sound and mixing different speakers covers more ground frequency wise. I think most just find a speaker that sounds good to them and run with it rather than actually trying out different combos.
Wow. I must be in the minority. I change strings when they sound dead. Lube the board when it looks dry. Otherwise it’s just a light wipe of a cotton cloth to remove dust and fingerprints.
Most amps can handle a 100% mis match. It may not be ideal but usually is considered safe. Now I’m not saying it’s good to do but in theory it should be fine.