Seeing that Nestopia is an excellent emulator and appears to be pretty much complete emulation-wise, I'm thinking you might want to consider adding some new features to compete with VirtuaNES.
The following are some features that VirtuaNES supports but that Nestopia does not, quoted from this thread
. I don't necessarily want all of these features myself, but they might widen your user base.
- Multiple language support (via plugins)
- 192kHz sound option (however useful, it's there anyway)
- Channel Equaliser
- Lowpass filters
- Adjustable Scanlines (0-100%)
- Ability to set refresh rate along with resolution
- Support for some additional special controllers