Well, Andy ...it's entirely up to your wife and how SHE herself, feels about it. It still has more than 4 years' validity left on it ... and t'would seem to me to be an unnecessary additional expense
- at a time when you're already shelling out a [not so] small fortune for her Spousal Visa - especially when any such alteration definitely ISN'T a prerequisite!
My own wife's passport, for instance, is still in HER maiden surname - and she has ILR.