Maybe I am misunderstanding you. Yes, 102.1 going active or alternative (which would reach Hinesville and Statesboro which have no modern rock choice) would be the best move, however, I was struck by your comment regarding I-95.
WIXV I-95 is considered heritage rock. Basically, they play about 200 classic rock songs over and over and always have. Obscure classic rock cuts on I-95 hasn't been the case in over 12 years. They recently went through a slight upgrade with a new voice for the station (sweepers), updated playlist (okay now it's 250 songs) and the demise of John Boy and Billy. Still, they have a very narrow playlist that focuses on the southern side of classic rock. You won't hear much from the prog rock artists like Yes, Electric Light Orchestra and deeper cuts from Rush. It's VERY mainstream. Tom Petty, Skynyrd, AC/DC 24/7.
Nationally, Active Rock is not doing well. That is why 106.1 is in the crapper and has been for a while. Notice that 106.1 playlist skews mostly 90s with very limited post 2010 (new rock) music which signals to the lack of popularity for new harder mainstream rock artists. For 102.1, I think the best bet would go in a Alternative Rock direction much like 101 WKQX out of Chicago. Cumulus would do a better job with Alternative than Clear Channel since CC tends to be more poppier an less rock in terms of Alternative. Cumulus tends to lean harder with their alternative.
With Rock 106.1 - I would suggest to stay the course. Changing an active rock station to alternative has proven detrimental for stations all over the country. Active Rock fans become irate if they turn on the radio and hear Lorde, Mumford and Sons, and The Black Keys replacing the more typical redneck white trash rock artist like Disturbed, Slipknot and All That Remains. Active Rock may be in the crapper for now but popularity between Active Rock vs Alternative swings back in fourth in the course of 10 years. Always has and always will. Still, straight alternative may not do well in Savannah which is why I think a Cumulus Alternative brand would be perfect since they tend to lean harder. You will hear some harder acts on Cumulus Alternative radio vs CC Alternative. Plus the big plus is the reach into Statesboro and HInesville which don't get 106.1 and have no modern rock choice.