I bought first Ducati when Peterborough was open and 30mins down road - they closed so now its 90mins to Cambridge for me but would travel further if needed so voted no However, I discounted buying a brand of bike this year due to complete lack of dealers generally but not due to location/distance of them
For me it is an issue. If something goes wrong with most new bikes now, they need diagnostics. They also need servicing by a main dealer if they are under warranty. If any warranty issues arise - then again we need that main dealer. If the nearest is many miles away as is the case with Ducati dealerships in south yorks now, its not really very good. A van would be needed (which I do not have) to get my bike to said dealer (and back). The less main dealers there are, means the busier the remaining ones will be - that can mean weeks or months to get a fix. Not ideal either. Its more than enough to put me off spending big money.
Living in C.London it used to be important over a decade ago, but there are no decent main dealers (IMO) here now, my bikes are no longer kept in London, I have van specifically just to move my collection around, and use the dealer who I feel will service it the best regardless of saving a few pounds.