Stockpages have their drawbacks. I rarely use mounts, so don't assume my comments are against using stockpages). I haven't really kept count, but I'm sure I currently use about 500-1000 Varios to house part of my collection.
Stockpages increase the bulk/weight of your collection more than mounts. Because the strips on the stockpages are fixed, you are limited in your layout (mounts allow for free form). For example, for sets that include a S/S, it's difficult to put the stamps and S/S together on same page without having the S/S sticking out of the strip (which is a very dangerous for the S/S).
If you collect a country/area by chronological or catalog order, I find stockpages are often not practical for modern stamps, which tend to vary significantly in size/shape. Before then, most stamps were pretty uniform in shape, so you could pretty much use 6/8-strip pages for the pre-1900 stamps, and 5/6-strip pages for pre-1950 stamps. After that, you really have to think things through to get the right arrangement of pages. Those are some of the problems I've encountered over the years. So as a result, my collection is sort of a mishmash of stockpages, stockbooks, and country albums.
So I can understand why many collectors go through the expense and time of using mounts. Mounts are not cost-effective, but if you like the look and freedom of using mounts, cost is not always the main factor that is considered. ***I have to admit considerable admiration when I view/purchase albums with mounted stamps.*** Of course, I just as happily tear the album apart to get to the stamps I want!

)
In terms of cost effectiveness, you will get some money back for the stockpages when you sell your collection. You will unlikely get any bonus for using mounts, unless they buyer plans on using the same album rather than incorporating the stamps into their own album. Either way, you will lose a lot more money using the mounts during resale.