As well as the cost, as big (if not bigger for us) is the limiting factor of how much we drink. Although our intake has risen since we've both been working from home, we've probably worked up to ~ at most 3 bottles a week between 2 of us (from little more than a bottle a week when on the road).
even buying frequently in 1's, 2's and 3's, the cellar size grows and I'm still grabbed by the opinion that so little of it is ready!
I'm through worrying though. We have a modest (in wine geek terms) stash (massive to non-wine geeks mind

), with some really good stuff. The variety is great and although there's probably too few 'quaffers' in there, the flip side can be some great mid-week wines.
In terms of style balance, there are safe ground favourites mixed in with new adventures (chianti at the moment via some auction purchases). Having specific expertise is useful around auctions, especially if that expertise isn't in the mainstream/big names.
I'm sure the balance works itself out over time and I guess the key trick is not to completely focus on one style. That and remembering that you can say no, even when it's a bargain!