Their bonus I think is fine, the problem is that they are not frequent enough.
In 105 silver chests and 6 jeweled chests I have received
92 loot
~80 buffs, i've used some but not much (at least 56 of which are the directly clicking related ones)

Buffs aren't terrible but with the short durations they serve the same function as saving silver chests for the better gold drop - to get you over a hump or the final push to beat an objective.

Back to loot -
Of those loot, I assume it is both equipment and trinkets. I've gotten 20 common trinkets, 6 uncommon. So, between 1/3 and 1/4 has been trinkets, of low power, and probably replacing equipment for someone. But since bonuses are multiplicative trinkets are going to be a very important part of late play/very deep runs. Why? 200% from enchants to 225% is a bonus but it's still diminishing returns. even my piddly 10% all dps from trinkets would increase that crusaders bonus by a total 10% on top of all their existing multipliers and be a similar (should be exactly the same) increase in damage. This effect then becomes more pronounced as time goes on and total enchants gets higher making each enchant contribute less. But trinkets rarely drop (at least for me).

I assume normal chest drops look like "loot/any/any" with a bias towards gold bags and buffs.
Jeweled chests are "loot/loot/any/any/any" with a bias towards buffs and at least one rare (which can be a buff).

Some change like
normal chests " Loot/trinket or gold/buff or gold"
Jeweled chests "gear/loot(favouring trinket)/trinket or buff/any/any" and not so heavily skewed towards buffs maybe?

Would go a long way towards the feeling of permanent progression and deeper runs as people start seeing their seemingly useless trinkets pile up into more meaningful amounts of bonuses.