The calculation is based on this:
15 points per city.
1 point per unit per level
1 point per 100 gold
2 points per building
3 points per hero, 1 per level
(Available in the wiki for ladder)
Why not just base the points entirely on gold value since we know the cost of everything or will assign costs to everything eventually in 0.9 or later.
1 gold = 1 point
hero value = cost to buy (500 for initial hero, whatever you paid for all others so you have to track the cost of each hero). Then add +25% value per level so a L2 hero is 125% of cost to buy, L3 = 150% etc. You are already in 0.9 going to allow buying leveled heroes so what ever formula you use for the level up cost can be the extra gold value if +25% isn't what you planned.
unit value = cost as an ally (right now this is something like 150 for a Wizard and 500 for RD etc). You'll have to put costs on all other units that aren't allies. But you'll be doing that anyway since you plan to offer mercs for hire so just work out a base cost of each unit as an ally/merc. We have months to tweak it once we know the costs of the current allies.
city value = rebuild cost (500 gold+income*5) For the sake of keeping things simple you can ignore wall level in the same way I assume you aren't going to count defense towers/lookout towers. Plus you'd need to track exactly whether the walls came that way from the neutral / another player or were upgraded by the current owner.
city production = 50% of cost to buy (based on 50% pillage). Also I would only credit players for production *they* bought and not for found production in neutrals. Or if you must credit found production credit it at a rate of 25% of cost to buy.
income site = income*5 (same as city income value on a rebuild).
items = cost to buy / value to sell. Many players asking for ability to sell items / buy items so eventually you'll probably add this feature too so why not go ahead and place a gold value on each item. Again there is months to get it all right.
KGB