OK, this is all IMHO, so take it for what it's worth (just one guy's take on the issue)...
The key to your dilemma is in your thread's title: *tactics*.
[Caveat: We've been playing our campaign since 1st-level, when 3.0 came out. We are now into epic.]
Something wee noticed long ago is there is a difference between what a group of PCs *can* do and what makes for a good game.
As soon as our level permitted, our resident mage started tossing disintegrate at all the BBEGs first round. That made for more than a few anti-climactic scenes.
The point is, I think it's important that a group (players *and* DM) step back and realize that the story is important. Not just the combat itself. Pacing the encounter out makes for better drama.
In our group, we came to the decision that the casters would stop starting out just focusing on the BBEGs. And the DM, likewise, wouldn't take advantage of the fact that we would "properly" wade through his lackeys first.
By mutual agreement, we've decided to allow the game to flow more like a dramatic story where we respect the DM's encounters and in return, he respects our characters.
Works for us anyway.
I guess what I'm saying is that there's rarely any fun, for anyone, when a character one-shot kills the main opposition right off the bat. By taking the time to allow the encounter to build, there is time for everyone to enjoy it.
My suggestion...
Rather than prep up *all* your boosts for a fight (turning yourself into a nuclear-powered-uber-monster), instead of casting destruction (or other "insta-deaths") on the BBEGs, just pace yourself. Cast only one or two of your preps and/or use a few "big bang" spells on other, lesser opposition first.
As a group, respect the DM's encounter and you will (hopefully) find that the DM will respect you back.
If this happens, not only will everyone have more fun, but you will likely start to see the scenes as more dramatic and cinematic in their flow.
At least, that's what we've found to be the case.
After all, how many movies/books have confrontations that start with the heroes ignoring the minions and taking out the BBEG first?
Whatever you do, I wish you all luck. Frustration, on either side of the DM screen, can be one of the biggest campaign killers.