For LOR's, does it matter which level class you took with the professor writing it? Would non-science LOR from a prof from an Intro to Psych class (1000 level) be less impressive than a letter from a 3000 or 4000 level class?
I think a lower-division letter is all right as long as the letter speaks beyond just grades and academic performance but delves into your characteristics, potential, and promise to being a great doctor. A meaningful letter is better than a filller letter. I guess it would depend also on the professional prestige the professor carries. It's not going to make or break your application.