I think this is a really tough hypothetical. Romney is a rational adult with broad experience. But he’s chained to conservative ideology as well as being the oligarch’s choice- he is an oligarch.
What would have been the effects of four more years of military adventurism in the Middle East? Troops in Iraq, troops in Syria, probably troops in Libya, potentially war with Iran (where else was that conflict going without a negotiation?) So, the deficit goes through the roof and there continues to be body bags and limbless soldiers on TV every day. The VA staggers even worse than today, by far. The national mood is, “Thanks a bunch, W!”
Could any amount of successful domestic policy overcome the negatives of GOP foreign policy? First, “successful domestic policy” would have been limited by GOP ideology. The public would still be languishing under an abusive health insurance system, imperfect as the ACA is, too. Taxes would be lower than they are now, but probably in a regressive way, aggravating the deficit and highlighting America’s oligarchic drift. OWS would have had far more fuel with which to catch fire.
So, what positives from there? Obama hasn’t really succeeded in his efforts for a national infrastructure rehabilitation. Under Romney circumstances, could he have done it, even if he wanted to? Probably not. Rather, I see cuts in food stamps and general austerity policies to pay for the wars. I don’t see what is so great about austerity for the sake of treading water- at least European countries can claim to be correcting their long-term problems with such policies.
There are probably positives I am not seeing. Good question of an OP. I’d be interested in being told specifically why I am wrong and why things would be better than my glum view.