If you have 20 spells in a 40 card deck, you should be consistantly flipping delver, and it will be well worth running.
The thing with those decks is that they are basically burn decks, supported by some kind of evasive threat (or threat that can be made evasive) that synergizes well with casting spells. The traditional problem the delver versions have had in cube (due to the reduced access to cheap cantrips and dig spells) is getting stuck with threat light hands (due to the extremely high spell count), thus not being able to apply any real pressure, while at the same time lacking the control mechanicsms needed to play a long game. I also think there is an issue with people drafting delver once (often run as the only spells matters cards) than horribly miss-building their deck, lossing badly, and cutting the entire archetype by the next draft.
Over here, red has a lot of "spells matter" control elements (flashback, burning vengeance) so playing a long game isn't a big deal. Red also has some of the only sweepers in the format (which happens to not target flyers) and some of the best spot removal. As a result, the deck is very good at playing out whatever role its opening 7 assigns it, and the extreme spells matter lists work.
The advantage of the prowess creatures and friends (
kiln fiend), is that the lists are a bit more accessible to draft and design for (though you still can, and probably should, run 1-2 delvers). You can run a more creature heavy "storm" version of the deck, with "free" cards that up the spell count:
riftwing cloudskate,
rift bolt,
gitaxian probe,
lava dart,
staggershock,
ancestral vision,
gut shot. When you combine that with a few creatures that get bigger for each spell cast, you can
teleportal,
blustersquall or
distortion strike in a big hit: than burn finishes them off. There are also some good aggro control elements with
talrand, sky summoner, and
young pyromancer. You could even try going full on storm with
temporal fissure.
White I think is a sub color, but can tie in all right with
stoneforge mystic getting
runechanter's pike or
leering emblem.
Geist of saint traft also fits in nicely in the deck, and the white flying token makers are very good at carrying some of that equipment, flipping delver, and triggering prowess.
Also, gather the townsfolk has been terrible as a spells matters cards over here, because you can't really exert pressure with it, unlike its flying brethren.