You know when you're already having performance issues on Heroku having a performance regression is not fun.
> […] handing that task to Sprockets instead of resolving internally […]
even remotely related to performance issues because of random routing? You're mixing two issues that have nothing in common.
2) The Rails release has performance regressions (i.e. in at least some scenarios is slower).
In situation (1) you don't want to add further slowdown so (2) is a bad thing.
Grandparent doesn't even blame his Heroku performance problems on the routing issue (although it is a plausible guess). Actually effect of the routing problem can be significantly worsened if even a subset of requests are slowed down.
Is that not the case?
Performance Regressions
There are performance regressions in 3.2.13 for both view loading and asset loading. Rails 3.2.13 changed the way assets paths are resolved, handing that task to Sprockets instead of resolving internally, which seems to be the cause of the performance issues.