HBA
Not UI things, but about your points:
It used to be, before all the key combos were changed a couple of years ago, that looking at the current speaker was one key - now it's two - control-\ - as I recall without being in SL to try it. I use that a fair bit.

I like my own browser, too - particularly for youtube vids as SL sends me to Youtube Brazil every time.

I never set Away, and have it disabled. I'm never Busy, either, as people are always sending me things (not as much now as in the past, though*) and I like being present and cheerful especially for upset customers (I don't do a lot of business anymore because I just abruptly stopped one day, but I do still get sweet lost customers occasionally**).

"Show last IM Conversation" or whatever it's called, is great, and logging chat and IM is useful to me when something is being discussed that I have to do. I used to, for, say, a custom suit of clothing, copy/paste the customer's desires into a .txt doc and save it, so I could refer to it whilst drawing, but now even if I crash or forget the chat/IM is still logged.

I've seen the bandwidth setting recommended to be 500 (specifically at Midian City), but never as low as 300. Kitty had success by making sure her texture memory slider didn't excede her card memory, which of course makes sense. I don't monkey with my cache much - only if something is corrupted (i.e. once or twice a year I might clear cache), and it's set in the middle somewhere, don't know. Going back and forth to many different accounts/worlds/viewer versions seems to make little glitches appear.

I've always thought I wanted a separate side screen for things like inventory, but I probably don't, really. It's supremely easy for me to block out portions of rl, so sl is even easier.

* Once during a snail race I was loping along when 4 or 5 big textures filled up my entire screen, sent for whatever the photo contest was then, I think. I lost the race, but I always had a tough time once the race moved up into the sky amyway, so it wasn't a huge loss.
**It's amazing how upset and sad people can be over something like an accidentally deleted virtual tent, but I always assure them right off the bat that whatever is wrong will be set right, and that they don't need to worry that I won't believe them. People worry too much.