Fran,
you don't have to ask "Why do I need a Tyros?"
Just find one, start to play it, go through all the styles, try all the sounds and then give yourself an answer.
If you think that you don't need one, then it's fine, but the answer has nothing to do with technical specs, IMO.
Andrea
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Korg Kronos 61 and PA3X-Pro76, Roland G-70, BK7-m and Integra 7, Casio PX-5S, Fender Stratocaster with Fralin pickups, Fender Stratocaster with Kinman pickups, vintage Gibson SG standard.