The 2012 election impact depends on how the campaigns spin it, but the political effects of striking down the whole bill versus part of the bill are quite significant for 2016.
The "must carry" provisions are popular and unlikely to be repealed before causing real havoc, which without some form of "must purchase" they will. If the Supreme Court strikes down only part of the act, they will have created a ticking political time bomb that will cause significant damage to the incumbent party in 2016 unless the bomb gets unexpectedly defused in time.
So, you're saying that if the whole bill gets tossed that it may propel Mitt Romney into the White House as the 45th President, but we'll likely be looking at a Democratic 46th President starting January 2017?
No. I'm saying that if we get a partial strike, it'll likely cause whichever party wins this November, be it Democrat or Republican, to lose in 2016.
If we get a complete strike, I see no clear advantage to either Obama or Romney.