Whole cities of buildings to bomb for points towards ye old bomber score, but which don't effect the rest of us being able to up? 
I actually think you're on the edge of something here.
When you look at the historical deployment of heavies IRL, it was generally in the service of taking out strategic targets. The RAF would bomb cities at night, the USAAF would bomb "pinpoint" targets in the day. Generally, these were NOT connected to Luftwaffe operation centers. Of course, there were notable exceptions; eg, D-Day support, etc.
I'm thinking that it's kind of a pity that, as Karnak points out, deploying them as they were actually used sort of "disconnects" them. However, it need not do so IF there were some underlying strategic supply model. I write this, btw, in total ignorance of the way the current strat model works (or fails to do so), as I don't much care for bombing myself.
For example, let's say the NITs have a fuel production center as one of their strat targets. If the Bish are able to take that out, resupply of fuel to the various operational bases is cut off. Each base could have some token capacity for storage that, once exhausted, is not replenished until the strat asset is back up. The same could be established for all of the other war materiels - aircraft, GVs, ords, ammunition, transport capacity. Of course, in order to instill the incentive to both bomb the strat asset and to defend it, people would have to understand the linkage and value of each type of strat asset. Essentially, to make bombing more relevant, we need an underlying economic/logistical model...
As for the tactical bombers, I think the best way to expand their use is to increase the scope of the ground war, introducing more/new ground vehicles, employing field artillery, perhaps even some generalized form of infantry.
