Being realistic, apart from the tires you have already done, there isn't anything that you can do that will be cost effective, to make any significant weight savings, you would be better spending the money one a complete new bike.

You seem to have the bike working as needed as you describe, would leave as is/ride as is, and only replace parts as/if necessary, and save for a new one.

Given the bike brand, take it you are in the UK, have you looked at the cycle to work scheme? as most employers offer this now, as it could be a way to get a cheaper new bike.