Isn't there a feat that turns a spell into a [good] spell? I don't believe there are that many really great spells to use for the +1 CL on the bard lists, so I don't think its worth focusing on.
The free extend can be used with summons... I still don't think its a great method. If you go SC, then you could pick up some buffs with it... For example, use Mindblank only once every other day.
Confusion? If you have a whole bunch of enemies? Charm Monster?
The problem is that although there's plenty of spells you could extend, most of them last as long as you want them to already, and extending them won't make them last through another encounter. Also, and Extend Rod is cheap, cheap, cheap, and people still don't buy them (except for ultra-paranoid wizards).