What I would like to see;

REF fixed; I know way overstated on the forums but here is my 2 cents

Liberty bell actually represent three things in the game:
1. Culture, not really important to game play but there
2. Loyalty well ran the Colonial Government
3. And an Independent mindset
Let face it since a European response took 6 months (3 months each way) the colonies got used to self government (esp, in British Colonies.) The British colonies were quite happy to be loyal, until a war in Europe made the king and parliament go looking for funds. The French and Indian war was a small part of a European War. But when it came to looking for ways to pay, they turn to the colonies.
Because Liberty bells do represent #2 above the R.E.F. therefore, should not be tied to it.
In my humble opinion the R.E.F. are : Large to start (yes it should take a large number of colonies to overcome Europe. Image if JUST New York had declared it independence), With a small growth rate tied to the number of rebels.

Fix the High Seas; yes I know the unofficial patch does this

so that any east coast coastal city can reach the high in one + a space turns, Spread the European powers out.

Add an Africa tab; Like the European tab

Give ship a choice when sailing from either Europe or the New World to go to Africa. What can you do in Africa? Buy slaves of course.
Slave Specialist: -2(may be -3 and totally useless) in city professions, -1 in Outdoor professions, cannot equip muskets, and cannot be educated (Not PC, or totally accurate, but it would reflect the mindset of the time.) Not sure the slave population should count in the total population since they are viewed as goods...Recruitment fixed cost 200-300 coins.
Possibly change the everyman is free choice to slaves become ex slave, which can equip muskets, instead of the plus 2 population

New Population System:

I never really liked food=population growth, starving people still play birds and the bees after all. And in a system where you can move food about freely it is too exploitable.
What I would to see is a new non exportable resource (pop growth) each settled colonist would produce one point per turn. once 200 points is reach you get a new colonist.
1 pop colony=200 turns a new colonist
5 pop colony=40 turns
10 pop colony=20 turns
20 pop colony=10 turns
This could not be used as an exploit to get more colonist after WOI, and more realist too

As soon as I get colonization in 13 days for my birthday, I will have that as one of the things to put as a mod. If you don't want me to make the mod I can help you make it.