Question

do bases individually affect reaction rate?
or is it the overall concentration that affects reaction rate...

Answer 1

First off, I dont know what you mean by "bases", do you mean lewis basis, or the nucleophile if so the reactants do come into play when it comes to the rate of a reaction but that is too broad of an assumption.

The overall concentration doesn't affect the rate of all chemical reactions, for example zero order reactions.

http://www.files.chem.vt.edu/RVGS/ACT/notes/rxn_order.html

Answer 2

When I say too broad of an assumption I mean that the lewis base is solely responsible for the rate of reaction

Answer 3

zero order reactions are reactions that's rates are independent of concentration, meaning you could double the concentration and the reaction would stay the same rate

Answer 4

An example of why it is wrong to say that the nucleophile dictates the rate of a reaction. Look at SN1 reactions

https://en.wikipedia.org/wiki/SN1_reaction

Answer 5

Hope this is helpful