Midweek is still very busy, iirc both were sold out last year when i went but it didn't feel as packed as it is for the finals. I did both the midweek and finals though last year and i honestly wouldn't do both again, it's WAY too much time in an arena watching dota but they hooked me in because of the random first blood drops lol
I want to go again this year, but i will most likely only get finals tickets and skip the midweek. Most of the better games are going to be during the finals anyway
Do both if you really like watching dota, and want more chances for first blood drops (i got about $500 worth of steam cash last year from selling them all) so its kind worth it if your RNG is good lol