Generally a system profits from more (virtual) CPU cores as it has more processing power at its disposal. An individual application may not profit as much from it, if it doesn't exploit parallel execution mechanisms, but even then other processes running at the same time (in the background which you may not even notice) could use the other cores instead of competing for CPU time with the first application.
Today's operating systems, desktop environments, and applications are much better at using parallelism than at the time the Pentium 4 appeared first, so even with a common application-centric workload scenario like yours, I strongly recommend enabling HyperThreading.
If you want to be certain if you benefit from it, you need to find or run benchmarks for your current setup. Everything else, including the above, can only ever be a rule of thumb. In my personal experience a desktop system with at least 2 cores is much more responsive than one with just 1.