I think that like many things DOM3 the answer depends on strategy, map size and other game settings.
I have succesfully used a maenid heavy strategy. In my experience they are not "next to useless." In fact, I think that the designers put in the extremely annoying maenid death scream to discourage us from using them
Maenids definately have their uses in combat. They are free and cost no upkeep, and they are berserkers. They are great for tiring out and eventually routing enemy troops. Fire at enemy troops with longbow centaurs while the maenids are engaging them. Use a bless strategy (nature for regeneration and earth to help with defense) and hold and attack with the white centaurs and other supporting troops.
If I remember correctly, a Pan in a turmoil 3 province attracts 9 maenids per turn, so if you can get a decent number of Pans in a province (I know they are expensive) you can quickly generate hordes of maenids. Properly equipped, your Pans can simulteneously summon lots vine ogres (also free and upkeep free, and they don't rout). That's two armies for the price of nothing.
As far as the money problem but consider the following. First, Pans are expensive but they can generate free armies (see above). Also, by having turmoil 3, you make it much more likely that a random event will occur in a province. This means that you'll hit the max number of random events much earlier in the game. I think everyone here agrees that random events are a good thing when you have the luck 3 scale. Also consider that temples are cheap for Pangaea (which leaves more for troops). If you buy temples aggresively your dominion will spread quickly. This feeds right in to the bless strategy mentioned above and the berserking nature of the maenids (and Pangaea in general). Berserking troops are at a great advantage if the are fighting in their own dominion; they will take initial losses, but they eventually rout most armies, even when outgunned. Finally you can use other scales to mitigate some of the income loss. Take magic drain 2 and growth 1 or 2 with a captive pretender. The growth scale gives you a little extra income back directly and a little more back by increasing the population.
This strategy won't work as well on larger maps, but I think it should work very well on a small mutiplayer map. Of course, as I said above, there are many ways to skin a Pan.