It's a bit like having Dread Shade and Phyrexian Rager, manawise. The draft dynamics make it so that heavy hybrids and light hybrids are really different from each other. If you look at all one-, two- and three-colored decks, you get the following numbers for hypothetical inclusion:
Dread Shade goes into 1 of 25 decks.
Phyrexian Rager goes into 11 of 25 decks.
Nightveil Specter goes into 3 of 25 decks.
Undercover Butler goes into 18 of 25 decks.
Psychatog goes into 4 of 25 decks.
Nightveil Predator goes into 1 of 25 decks.
So a heavy hybrids is close to a splashable gold card in flexibility. The question is, what kind of decks you want to promote. In m cube, decks seldom go into a third color. You still get some 3+ colored deck, but just because there are synergies, not because mana symbols force you to do so. So in my cube, Nightveil Specter is more flexible than Psychatog.
Yup. Just keep an eye of how many cards from that section go in decks of the five colors, so that you don't end up with 20% more cards white decks can play compared to red decks.
My philosophy is to always look for a more flexible option if you don't lose much else. That opens up more possibilities in drafting. I've increased my colorless section to 55 cards, which is over 10% of my cube, not counting fixing - I even have the Talismans listed as hybrids, as that is how they usually play out.
Colorless cards, just like hybrids, help you actually finishing a draft with a mono colored deck, but they don't make you want to do it. More importantly, you need to enable cool and strong mono colored decks. People draft mono red and mono white in the mtgo Vintage cube, because they work. They don't draft mono black really, because it has no real strategy. Then add some signposts or payoffs to lure them in and mono color decks will show up.
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