This whole line of thought has been marinating in my brain lately, and I believe it's about to spawn another.
The idea of spells having their own levels, and having a range from 0 to 9 is, of course, a hold-over from previous editions. Also, it, like everything else in the game, is a contrivance for the game's sake. So, changing it is just a matter of volition, as is evidenced by all the alternative systems (spell points, skills-and-feats based casting, etc.).
Here's yet another suggestion. Let's consider the wizard to be the archetype of magic spell casting, the way a fighter is the archetype of combat. Instead of spells being levels 0 through 9, why not 1 through 20? In other words, a 1st level wizard can cast (up to) 1st level spells, a 5th level wizard casts (up to) 5th level spells. After all, just doubling all the existing spell levels comes pretty close to the same thing. There have to be, say, some 5th level spells that are a bit more powerful than others, and some 6th level spells that are a bit less powerful than others; these would comprise the 11th level spells on this system (the other 5th would be 10th, the other 6th would be 12th, etc.).
This would take a little tweaking, because all the spells that exist would have to be "stretched" from a 0 to 9 template onto a 1 to 20 template, but then there would be a straight progression. A 15th level wizard could know and cast, at best, a 15th level spell (which would, of course, be roughly equivalent to one of the current high-end 7th level, or low-end 8th level spells). A similar thing could be done for other spell casting classes.
What about the bard? What about the paladin? Etc. Either we have spells as we do now, that can be cast as different level spells by different classes, or, we use something similar to the BACL, BDCL sytem that you've proposed, or we combine them.
Perhaps this isn't a good idea for the 3rd edition of the game, I don't know. Maybe it's too drastic a change. But, another thing I like about it is that it provides a framework for spells beyond 20th level (or, in current terminology, beyond 9th). I don't much like epic spells. I think that meta-magicked spells taking up slots beyond the 9th level slots is a good idea, but I see no reason why we can't extend the damage dice caps found in the DMG, and just create more powerful spells (including things like Greater Wish, that would be proportionately more powerful than a Wish, as a Wish is to Limited Wish, etc.).
Dave