The only constant is change, right?

Way back when I used to principally fly United, but I didn't know much about miles back then and an economy r/t to Europe was about the height of what I redeemed.

Then I started traveling more for work, settled on Delta, hit Platinum status. Then the devaluations started coming. I spent my UA balance to zero or close to it. I have a few hundred thousand DL miles but will use those on VA to SYD and that too will be near zero.

Now I fly AA/US almost exclusively and have a healthy balance of miles with them. Those miles get me much of the kind of travel I like to spend miles on (international, premium cabin) But of course diversification is always a good idea.

That's why I have small balances with a few other airlines -- AS (25k); LH (55k); AV (45k). I'm now trying to figure out what my next step(s) should be. Should I try to build up balances in the "other" programs? AS has some interesting options/partners, but nothing other than a domestic economy r/t for 25k. Similarly with the others -- sure I could fly UA BusinessElite one-way for 17k miles using LH, but other than a few niche redemptions, I need more miles.

So should I start building up these other balances? (Buying 2x1 miles with Avianca?) Should I "circle back" and build up UA/DL, or leave them for good? AA/US have been treating me pretty well but I feel like I have all my eggs in one basket right now.

We have no "wish list" travel right now -- the trips we want to take (Ireland, Australia) are either booked or will be with existing miles. So I would be building up miles speculatively for now.

For what it's worth my wife has similar balances so the total miles we have are 2x the above. For our longer vacations we travel with the kids (two of them) so we probably need 4 seats on a given flight. Hard, but not impossible.

Thanks in advance!