Hummmmmm..., 90 miles there/90miles back would probably be quite a long day and not allow for much of a detour for nice roads and then be rushed at the place. It says 90mins for the tour, but there would be other stuff to look at like you say (Visitor centre). I'd be tempted to suggest staying over nearby. So could take a long way up Saturday (Wye Valley/Malvern Hills) then back across down through the cotswolds the next day (Sunday) after an early-ish tour and lunch.
Problems are it'd be luck with the weather, and you do have to book well in advance, (approx. 3months atm) so you've no idea... Could probably comfortably mini-bus it in a day out of season which seems like the best (but no biking there ) option..
I think riding up for a day/overnight it would probably be best without booking and going to the exhibition centre and/or national motor museum. So needn't worry about weather/pre-booking. Likely next spring/summer..
Mini-bus for the factory tour on a Sunday January/Feb. Could be a nice respite from the shorter days and a motorbike themed day. Anyone fancy this? I can drive, have driven a knackard old school bus round the block once before..
(Not to mention M4 karting's mini-moto's for a Sunday in Jan/Feb. also one to book a bit in advance.)
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