In reply to Sam W:
> The two key reasons for asking the question are firstly I'd like to upgrade both bikes, but can't afford 2 bikes at the spec level I would like. Similarly, if I split my budget in two, I'll end up with two bikes that aren't much better than what I have now.
OK, you want a new bike at a decent spec.
> The second reason is space, I would definitely be pleased to get down to one bike and free up a bit of room in the shed.
Makes sense.
> Take your point on a second set of wheels being a significant cost, but I do think it should be significantly cheaper than a whole second bike.
Correct, but...
> Differences in costs associated with wear of parts I can live with, ...
Not sure about your logic here: Twice the wear on one groupset is the same cost (long term) as spread over two. Of course the length of 'long-term' may be significant or not depending on how much you use your bikes.
I get the impression that you really just want a new bike and you're happy to just have one. Nothing wrong with that. Personally I like the convenience of having a mucky/sensible/gravel bike and a nice clean wizzy bike (currently on the turbo in the house).
One other though: Resilience: My nice bike is labelled 'all-road' (max. 35mm slick tyres) but I wouldn't really want to take it on some off the rocky off-road places (in the Peak District) where I take my more robust (feeling) gravel bike (45+mm knobblies). There probably are bikes that could comfortably do both jobs, but would they be 'jack-of-trades' or 'masters'?
Post edited at 15:04