ability to specify _all_ events by name, i.e. if I want "SNOOPQ_REQUESTS_OUTSTANDING.DATA" I can just say so, instead of having to look it up and then having to specify the unintuitive "r01b3".
Being able to specify an output file that is nice ascii text, dumped every time a counter hits a certain threshold. This is probably possible with perf, but the perf --help is hard to follow.
It would be nice to have a perf-only mailing list, but I guess that will never happen.
It would also be nice to be able to build perf without having to download the entire kernel tree, I often don't have the space or the bandwidth for hundreds of megabytes of kernel source when I just want to quick build perf on a new machine.