RAGBRAI riders will not steal your bike and I don’t think many professional thieves haunt RAGBRAI. Never heard of any. But town kids might take your bike for a ride and leave it where ever. This is also rare but the smallest, lightest, simplest bike lock you can buy will be enough to convince them to take some other bike.
Even if you hit the road at 6am when the ride officially starts each day you can ride pretty fast most of the time. Traffic will be alternately dense and sparse most of the day except through towns and other bottlenecks. If you are absolutely type A on steroids set on having everything, riding speed included, exactly your way, all of the time, then you are going to hate RAGBRAI. If you chill out, roll with the punches, and just enjoy yourself boy, oh boy will you ever enjoy yourself! It’s your call but do it right and you will ride as fast as you want a lot of the time and enjoy your time in Iowa all of the time.
There might be a line of people waiting for Jamis gravel bikes, assuming they are back this year with that program. Say hi to their Eskimo dog if visit their booth! God bless them but people do ride the gravel on 23s and live to tell the tale with smiles on their faces so you could too. Find some gravel roads near you and get some practice. Generally there are car compressed tire tracks that you can follow. If your fancy bike will take 25s or 28s (and I know that a lot will not) consider bringing a pair of “fat” tires to run that day. I mean you can run them all week just fine but little chance of convincing most of you of that. I have done every mile of RAGBRAI, every year I have gone, on 38s and it doesn’t hurt a bit! They also weather the slings and arrows of outrageous fortune you run into occasionally on paved road nicely too.