I agree we have very few gravel roads in England but using a combination of towpaths, forest or woodlands trails, disused railway lines etc. we often put together 70-80 mile circular routes without too much trouble. Yes, we encounter mud but it's not a big deal. I've only ridden gravel for 16 months but so far my 35mm Marathon G One All-round have coped with everything.
Now that I own a bike suitable for gravel I've realised these are very adaptable machines. I'd go so far as to say my Kinesis ATRV3 is a five-in-one bike. Gravel, winter, touring, commuting (given secure storage) and summer road bike. The first three use the same set up, commuting I would just add a rack and for summer I would either swap wheels (very likely) or tyres (very unlikely).
The only reason for changing wheels/tyres in summer would be speed as to hit the 20+ I need on occasion is very tough on 35mm Marathons. Acceleration isn't as good as my Cervelo which is a downside for group riding.
Overall if I could only buy one bike it would be a gravel bike. Very versatile.
