I used to dig on the plant substrates...but I'm starting to rethink myself. For one, plant substrates are only really beneficial (if at all) to heavy root feeders. Therefore a good number of common plants such as anacharis, java fern, java moss, anubias, rotala, water sprite, hornwort, cabomba, et al, which don't have heavy root feeding requirements (Or even roots at all) get little from such products. From what I know, these plants get more than enough of what they need, nutritionally speaking, from the water column. So liquid fertilizers are what benefit them the most. The substrate is entirely inconsequential.
That leaves heavy root feeders such as cryptocoryne, swords, vals, etc as being the only plants that would seriously benefit from a specialized substrate. (Again, if these substrates actually do anything at all except cost more money.)
That being said, consider the fact that even with specialty plant substrates, it's still a good idea to use root tabs with those plants. (I used Onyx Sand in my Amazon tank and didn't notice any significant vitality in any of my plants until I gave them root tabs.) So when all is said and done, you can get amazing results with simple gravel and/or sand and some root tabs and some quality liquid fertilizers. A little CO2 never hurts either.
Just a few thoughts to consider.