I would say that yes it could improve the performance but then you will loose features that are only available on tunnel mode.
Also you can enhance the performance on tunnel mode if you do a link aggregation bettween controller and the switch core which you got it connected...
Also if you got access switch in which you are connecting your APS
Let say you got a 24 port switch with 20 APS, and your uplink is just a 1 Gig... not even if you are bridging will improve the performance...
In that case you will need to do a link agg between tha switch and the distribution switch... or having a s2500 or something similar with 10G of uplink...
So at the end it does DEPENDS on your network, and how you build it... it will not Magically improve the performance...
I do have most of my clients with tunnel mode, but i advicse them to have Link aggregation everyone to improve speed... from the access switch to the distribution swithc and form the distribution swithc to the core switch and from the core switch to the wireless controller...
If they got 10gigs uplink then use it. It also depends on how many APs you got... if you got like 5 APS you migh not need to do anything... if you got 500 aps then you will need to do stuff to tune your network.
Just my 2 cents
Cheers
Carlos