As long as you don't have a spool or welded diff in the front you won't notice much, if any, issues driving down the street if the t-case is in 2wd. Well, I guess if you have some crazy driveshaft angle or something you may get some vibrations and some extra wear but you are just rotating the shaft and putting any torque through it. Keep in mind that a lot of 4wd trucks over the years have not had locking hubs, this goes for part time and full-time 4wd, and from the very first 4wd trucks to modern stuff. The trucks made within the last two decades with some sort of locking hubs or front axle disconnects were primarily just for fuel economy reasons.
It was stated above, but a buddy ran drive slugs on his rig and just pulled the drive gears out and put the caps back on when driving long distances on the road. Probably took 5-10 minutes so not a big deal when you drive 1-3 hours to get to the trail once or twice a month, so not like you are doing it all the time.