I've played about 5 games now start to finish and what I found is that some of the late game spells take too long to research compared with their "technology" counterparts.

It seems tech points and arcane points should be somewhat balanced (as we see the costs of units/traits/builds/etc is very comparable point for point)
Technology however trumps magic quite considerably as far as your return on investment.  You can get  5-10 techs in the time it takes you to get a spell.  (comparing the full arc of cheap ones, medium ones, and heavy ones).

In particular level 7+ spells are insanely expensive, and the spells you get barely superior.  I think there needs to be some serious re-balance work here.

Many were taking me 20-30 turns, some even 40 or 50 (my arcane was about the same as my tech  floating from 20 to 50 or so through the mid to lategame).   The techs however were coming every 2-3 turns on average and I was almost done with them long before I was even close to finishing the arcane side.

Gold seems to be in a major shortage as well compared to the other resources (metal/materials) towards the endgame.  I find myself trading away 80% of my metal and material till no one wants it.  Even attempting a game where 80% of my cities focus on generating gold I found myself using it far quicker than anything else.

I propose

#1 Make endgame buildings more expensive resource wise.
#2 Have somekind of internal market where you can sell things for gold (2 material = 1 gold etc).

This would mean you can channel severe surplus into something psuedo usefull, as well as avoid many frustraiting "1 gold short" situations. 

Cheers