As M Merckx rightly said, don't buy upgrades, ride up grades. Saving 200g on a pair of wheels will save you precisely bugger all time on climbs. If you had £3.5k to spend on a set of Lightweights you wouldn't suddenly start bagging Strava KOMs. And the law of diminishing returns applies, the more you spend the less 'benefit' you get for the money. Ride more and you'll get faster. You have absolutely no need of a back-up wheel set for rain. It's not like you're wearing your rims down & any decent wheel set will be perfectly OK in all conditions.
That said....I would happily recommend Hunt for factory built wheels (e.g...
these rated 5/5 by road.cc). Also JRA, the likes of DCR for handbuilts.....