This is just an idea for technology. Buying tech with gold is ok... kinda... but i think there are better options. IMHO, It should be more similar to the way traditions works. But off course, there are more technologies than traditions, so i think an point system could be used.
Those points would represent the insight capacity of the society, or the actual application of new knowledge in the institutions and daily life.
A country would get points from their researches work, in each of the 4 categories, as the progress for a new technological level is developed.
In the image a) is where you get a new point, and b) the current new level, new technologies to the pool and bonifications. So, technologies would appear in b), but you would buy them with the points you get in a). That way you also get something worthy while leveling up.
The ammount of points you have for each category could be show in c)
As option, some very powerful technologies could cost more points and that cost could be show in d)
Some considerations
-In 0 level you would have some starting points in each category. In that way the experience would be similar to the one we currently have and countries wouldn't be technology naked.
-The system could be used to add more flavor to heritages. For example, sparta could get more points in military tech, athenas in civics, etc. That way your nation identity would have impact not only as a bonus, but in the very path of development you follow.
In anycase, this is a very early unpolished idea. I had some fun thinking about it and wanted to share it with the community.