Turrets and Wards: Grant assist to most damage
It is pretty annoying that turrets and wards depend on (most recent) last hits, rather than who dealt the most damage.
There is not the competitive aspect that baron/dragon/jungle has, nor is there the skill aspect like with minion last hits
If a laner takes 95% of the turret HP, and then has to back - someone else on the team can come and do the last bit of damage while the laner is away, and the laner gets no assist gold from it at all.
The same applies to wards in a way, someone can do 2 or 3 hits on a ward, and then someone who did not do anything does the last hit, and gets the wards-destroyed counter for mastery rankings as well as the main kill gold.
dealing the most damage should in my opinion grant an assist at least