I'm currently playing a drd-3/wiz-3/mt-2 and I have to agree that he excels at flexibility. The druid spells provide some significant options that a cleric wouldn't have. For example, summon nature's ally spells are almost always preferable to summon monster (expecially with Augment Summoning). I've also taken Practiced Spellcaster (wizard) and plan to take it again at 9th level.
The problem is lack of punch. The character can do a lot in a fight, but rarely has a spell that takes out the bad guys in one shot (though glitterdust sometimes does the job).
Any suggestions?