Give up trying to lighten the bike, it sounds like you can’t afford to make a significant difference and a 26lb full susser is hardly unraceable. I came 4th in Oktoberfest 8 hr pairs and 14th at 24/12 racing solo on a 26lb full-susser this year – I could have done better but it would have been down to more training not a lighter bike.
You admit you’re not as fit as last year, why aren’t you riding as much? Address this. If it’s because you hate riding in bad weather, spend the cash on things more likely to make you go out. Goretex shorts, some overshoes or Goretex boots, some crud catchers. Hate maintaining your good bike and wearing stuff out, get a dirt worker to help clean the bike trailside, or invest in a cheap singlespeed hack MTB or something. If you find your local trails boring, spend the cash on going and riding somewhere new and reinvigorate your interest.
Spending £500+ to knock 2lb off your bike is ultimately going to be disappointing.