The answer, to me, has nothing to do with politics. Polls show that the public cares little about the issue, is fine with the idea of raising money from small donors, and isn't likely to hold it against Obama ... and certainly not once the attention dies down.
But I think the larger question as to whether it was the right move for Obama boils down to this -- come early October, will his staff be sufficiently focused on get-out-the-vote efforts, or spending too much time raising more money for last-minute ads? And will the grass roots be busy raising $25/person or arranging voter caravans and neighborhood walks in the last few weeks? For all his successes in turning out voters for caucuses, there's no question that Obama struggled turning out voters in the big states (Ohio, Pennsylvania, California, etc.) in the primaries. That could be a function of the fact Hillary often closed strong the weekend before each Tuesday, but you hope the quest for $300 million doesn't distract from the traditional micro-targeting that almost always proves decisive, and certainly did in 2004. Ideally, Obama raises enough in the next two months so post-convention it's not as much of a distraction, but let's hope the money advantage he'll almost certainly have pays off. Remember, the last month of primary season, Obama outspent Hillary up to 3-to-1 in most states, and it didn't necessarily work.