I own a Club Tour and used it for over 2 years in gravel spec , i.e stripped down of racks and mudguards and with 35mm or 40mm more gravel orientated tyres.
It was very capable in this spec and I trained for and rode the Dirty Reiver 200km on it around kielder Forest. (mines in the pic in the brochure. )
I bought mine with Cantilever brakes, and found them ok, but I did push the boundaries of where the bike could be ridden and thus braking too which could be fun in the wet!!
I would say stick with 700c wheels , there is loads of clearance on the Club Tour, and you could even leave mud guards on as well.
My Club Tour is now back in road spec as its used as my commuter and shopping bike/ Touring bike/Winter Audax bike , and I bought a disc brake gravel bike, I very nearly bought another Club Tour , as was going to have one in road spec and gravel spec, but with mudguards on it will do both jobs really well and did ride it like this for a while with gravel tyres on.
Its not particularly sporty feeling , but its not supposed to be.
An alternative could be a Mercury , I had one of these, it rides really well, feels sporty handling, and the Roholf would suit gravel dirt,
I had mine built up as a lightweight build and without discs , and wish I had chosen a heavier build and discs, my rim brakes would not take tyres above 28mm . But the Rolholf is not a sporty gear change unless you go for the new trigger shifters so descending fast on a gravel road taking the hands of to change gear not that easy, fine on tarmac. I do miss this bike.
I sold the Mercury and a mtb and cx bike to fund a gravel build, at the end of the day any bike can be ridden on gravel as long as the tyres are over 35mm to 40mm, having the low gears on a Tourer should not be underestimated esp if you plan to carry any kit, something most current gravel bikes miss completely.
( My cx bike was carbon and so stiff it was a not ideal for gravel riding but good fun and was great for short rides , a great bike did the True Grit in Yorks on it a few years back on its first running , , but was a touch too small for me frame wrong size and on Cantilever brakes too ) , but riding the steel frame after this bike made me realise how comfortable the Club Tour is.)
Hope that helps a bit.
The Club Tour is a really versatile bike.