I remember years ago we had to take the old wooden spoke wheels from our farm wagon down to the creek and let them soak for a few days because the spokes would dry out and they would become loose. I have a 1925 T with wooden wheels. I store my car in a unheated garage and I never get it out when it's raining. Is there any danger in the wheels getting loose from drying out.
If they're worn out, maybe, but good spokes will stay tight when dry. If they don't it's time to respoke.
In the day folks were known to soak wood auto wheels in water to get them to tighten up but it is a temporary "fix" at best and they just dry out and shrink again.
Another option today would be to soak or paint them with auto antifreeze. It will swell up the wood just like water but will not dry out and shrink up again. But again, it is a patch job for wheels that probably need to be rebuilt.
Every 3 to 4 year I put the wheels in Sunflower oil for 1 day and it works perfect.
There a variety of methods to retighten loose spokes soaking is very temporary. Sheet steel shims can be driven between the spokes at the hub, there are split washers available to insert between the spoke and the rim, also if the dowel end is warn (on a demountable) it can be drilled out and a new dowel pins can be glued in.