Well, let's go.

And previously sorry for my English.
On citiesinmotion.ru we created RealPriceStandart for transport and infrastructure. I talk little more about this - may be this will be interesting for you for realisation in CiM2.
Our main idea was create realistic ratio for prices on transport and infrastructure (trolley wires, tram rails, tunnels etc.). We counted the prices from real money to game money (1cim ~ $75) and as result we have got pretty realistic view. For example, trolley wires costs 56cim (~$4200), tram rails - ~180cim (~$14000) for segment. In this case, for example, price of bus MAZ-103 - 1650 (~$125000), LAZ-A183 - 2510 (~$190000), MB Citaro - 3000 (~$225000); tram KTM-19A (with IGBT) costs $325k - it's 4340cim, and so one. This Standart has some nuances in regard metro and modern trams (Citadis 302, for example), but if you are interested - I can send you PM with our details.
Second very important detail: maintenance cost of transport. As I understand from game video, now maintenance cost of trams will be lower than buses? It's great and very realistically. In our formula maintenance cost depends on many things: mode of transport, reliability, control system (for e-transport) and so one. This allows for realistic ratio on maintenance cost. For example, new tram with IGBT costs more (sometimes very more!), than old tram. However maintenance cost of new tram lower than old.
Third: consumption of transport. We create complex formula for electro transport, what include total mass, max speed and engine control system of vehicle. Now we works on some formula for buses, what well be include power of engine, Euro-standart and mass of vehicle. Again, if you would be interested in it - I can send details in your PM. I talk this, because may be you already decided with your economy system.)
Fourth: capacity of transport. We consider it's a simple formula. Buses and trolleys - nominal capacity (5per*m^2)/2.2, tram - nom.cap/2.4, metro - nom.cap/2.5. These values very good looks in CiM: not much, not enough.
Well, as I said, if economy system of CiM2 still not defined - I can offer you our help.
Now a few suggestions.
1. Trolleybuses, please

With normal catenary (and trams too), and really individual more of transport.
2. If through stop passes some routes, what follow in the same direction, passengers have use the first bus, what came. Well, I find the difficult to explain this, sorry. But I hope you understand, what I wanted to say.
3. User should be able to choose the number of cars on metro train (3-8 cars for example) and trams (1-3 cars or 3-8 sections) in depot. If you buy two identical tram, you must be able to merge it's. If the design of the car can do it, of course.
4. In depot need "repair shops", where we could restore old vehicle. If, for example, condition of the bus = 40%, and we don't have money to new bus, we just can repair this old bus (+30% condition, for example).
5. Tram tunnels and overpasses.
Here. This is a small part of suggestions from russian community, but my post is big.

I'll add more later.