I think the best way to think about Ritual without trashing is basically as a second duchy pile. For $8 over two turns & buys, you net 3VP for one dead card. Compared to provinces, that is woefully inefficient and is not that great ... except that you should often find yourself in situations where you do not care about the coin efficiency of the other piles because they are close to empty anyways. Build the Rabble engine, then slowly churn out 5 VP/turn for 8-10 turns. Or go for Fteller/Legion payload combo on an engine and again slog out a bunch of VP. We routinely will accept all manner of spare VP as methods for engines to be more viable (e.g. weak Gardens, Silk Roads, Fairgrounds, and no discarding Tunnels), this is just a low end version of that for any card you like to trash.
Now Ritual shines when you can cheaply gain high value cards to trash. An action, a draw, a buy and $4 is actually not that bad for good VP.:
Mint can nab you up 8 VP per turn with a Ritual. That is exceedingly good for building up points without ending the game on a colony board.
A holy host of things (like Bag O Gold, Explorer, Charm, Duplicate, Windfall, Tmap, Page, Hoard, Tunnel, Msquare, Ssayer, and Governor) can all gain at least Gold; some are not even terminal.
Peasant can situationally provide you with "free" high value cards to trash and there are a lot of methods to get cheap actions - Ferry, Peddler, Quarry, Charm, University, Pilgramage, Advance, and Prssn
Even Transmute can be part of an efficient build to pile the curses with Rituals for a lot of VP.
Sure X/(4+X) is not going to be as efficient as the stock green (it ties or loses to every VP pile on raw cash efficiency) ... but it does work if any of the cards in the kingdom can give you value more efficiently than raw cash (most Ritual boards will have at least one of these).
Beyond that let us not forget that Ritual does a few other things for us - it is one of the few ways to trash out unwanted trashing. Possession & Forge? Ritual away the Forge. Have an extra estate in Rebuild mirror? Ritual it away to stop mucking up the Rebuilds. Forced trashing with Golem, Tr, or Herald? Ritual is good for what ails you.
Likewise, if you need to score points on Mission turns? Ritual is there, particularly if you have efficient gains. Need to trash out Gold, Silver, or singletons for Bandit Forts & Wolf dens? Ritual.
I have not played it yet, but I think there may be a nice combo with just Msquare. Buy some Silver & Msquares to start. Trash an estate (no net VP change), gain a gold or two, trash a Gold, gain 5Vp & gain more gold. Rats likewise seem to be nice - one initial $4 & one initial card can let you cycle Rats -> Ritual (trash Rats) -> Rats(trash curse) -> Ritual for $4 each. $4 for 4 VP, non-terminal is better by far than Dlands.
Ritual, like a lot of Empires, rewards you really highly for tactical play - use it sparingly when opportunity arises rather than building a deck on it and for boards that muck around with cost efficiency. Certainly it will not be worth building a strategy around, but you should routinely expect the odd busted hand to become a Ritual when it aligns with a defunct card (e.g. $4 & Moneylender near game end).