yup, starters are to grow yeast cells. higher than 1040-1050 starters will encourage the yeast to make beer, not grow cell counts. I'd stick with stepping your starter from vial to 2L to 1gal (or whatever mr.malty recommends).
Are you interested in a malt only barley wine or are you willing to use adjuncts to get there?
Growth, yes, but even more so, starters are for
yeast health.
I do not fault the logic of the OP. It almost makes sense to create an environment that is similar to your wort. However, in practical terms, that logic fails. Ideally, you want your starter around 1.040 and on a stir plate about 24-36 hours before you pitch. The constant gas exchange that occurs on the stir plate basically super-charges your yeast. They will be healthy, and ready to ferment whatever type of wort you throw at them.
The large (+1 gallon) starters are really like conducting a mini fermentation. Since you do not have that constant gas exchange to facilitate health, you have to rely on the yeast to bud and multiply. If you are in this situation, I strongly suggest making your starter a week ahead of time (stepping up if neccessary) then once the mini-fermentation completes, put it in the fridge. This makes it easier to decant and pitch. If you try to decant while the yeast is still working, you actually select and discard the least flocculant yeast (the ones that were best suited to due the fermenting in your barley wine).
Joe