How will I benefit from upgrading my node to 0.21.1 if I am not a miner? Should I wait to see what happens with signaling?
Not at all - although if the soft fork is confirmed you will need to upgrade before November when it activates to be safe.
Although there is a bit of benefit if the pools see lots of node on 0.21.1 might make them more confident to start signalling.
Also note a couple more pools have upgraded. F2Pool (16.3%) and Foundary USA (5.43%). So about 25% of hash power is signalling - 1/3rd of the way there...