For background, I am very much a wheels on the ground, natural trail riding rider, all be it at 80kg.
On my 29er Short travel FS bike I have some cheap OEM wheels which, whilst ultimately fine, weigh in at around 2.5kg without tyres.
Looking around the web, it would appear that I could get some CX disk wheelset of the 1.6-1.8kg for =< £200. This drop in weight would most likely be quite noticeable.
Would this be complete folly or is there method in my madness? After all surely wheels get a easier time on a full sus bike than a rigid CX bike...
On paper, a CX disc wheelset is a lightweight 29er MTB wheelset. However... The one important distinguishing factor will be the internal rim width. Typically, a 33mm CX tyre will usually be fitted to rims with an internal width of 19mm or less, where a 29er MTB tyre will usually be fitted to rims with say 21mm or more internal width. If you run an MTB tyre on too narrow a rim, it can have an overly round profile (causing a lack of edge bite and excessive tyre roll), where a CX tyre on a rim that's too wide would have an overly square profile causing extra drag and making it a bit of a pig to turn into corners.
All that said, my CX bike came fitted with Easton ARC24 rims though, which are a 24mm internal width MTB rim, so there's some scope for overlap here. Even on an XC MTB I wouldn't run anything narrower than 21mm internal width these days myself though.