i've got a little bit of play in my bottom bracket. It seems ok when I've tightened it all up, but don't want to overdo it if it's a bearing issue. It's been in there a fair old while and has covered a lot of gritty, wet and grindy miles.

Replace the bb, or stick with tightening it up ahead of some clear cut damage?

have you taken the cranks off and had a feel of the bearings? if you can feel it there then its probably worth replacing. if not then just nip it up. i used to be a bit blase about bb bearings but after my brothers seized and tore his threads in his frame i dont take any chances!

time to buy some new ones as back up. Try a clean and regrease my hope stainless lasted 3x shimano with a couple of regreases but non drive side failed after 2500 mile with two winters.Testing enduro in hope cups at the mo (crossing fingers as I live in a gritty area)

pop the seals off the a stanley knife of thin screw driver and clean them up ,then cover them in grease and put the seals back on, should get a good few months out of them.

The bearing arrangement in the HT11BB is the same as a headset. Would you throw your headset away every time it developed "play"?

As above, check bearings for smooth rotation, relube if required, and readjust preload.

I was going to replace mine last weec(Hope stainless) after 12 months or so but took LBS advise to do what spock did above, leaving them within the cups and on the frame. Used Teflon grease and Finish Line wet lube. Careful with crank preload and all is well. Very slight play but good for a while yet.
Apparently you're meant to clean & lube them every few months for warranty…