Panici:
Any ideas to further filter the signal with hardware, so I can actually use the time between pulses that pulseIn gives me?
It would make for a more accurate display.
The way you are using pulseIn() is giving you the length of the tach pulse, which is the main information you need. However, if you want work with the time inbetween pulses you could have a separate timer that is reset everytime a pulse is read (I wouldn't use another pulseIn() because of the way it delays the rest of the sketch).
As far as a hardware filter you'd want either a low pass (set just above the frequency you are limiting to in the sketch) or a band pass filter (with the low end of the band being the frequency correlating to under 1 RPM or whatever minimum value you are interested in), and a passive first-order implementation could be sufficient.