I play both for the exact reasons you mention here and don't think it takes a ton of time. They have different content cycles and SWTOR especially doesn't require lots of dedication to stay current. I pay for WoW sub in gold and use the money I was spending on WoW to keep my sub in SWTOR active. I do everything I care to do in SWTOR and then mostly play WoW. I still stop into SWTOR once or twice a week to check the GTN and do some of the quick heroics. When 4.1 comes out I'll cut back on WoW for a week or two and do everything new in SWTOR. It works well for me and I almost always have something I actually enjoy doing in one of the two games.