Sorry IMJ don't have an Iyonix (yet). So my argument is *not* based on me having to justify a purchase.
The reality of the "kit" that's available is that VA on a typical PC runs slower than RISC OS on a "real" SA or Kinetic RPC (except for harddisk access). There is faster alternative available (the Iyonix).
The appearance of Iyonix has had a few tangleable benefits even for users of other Acorn style machines (for example the Update C/C++ tools, updated 32bit library, modules to support some Iyonix features on non-Iyonix machines, the pop-up printer system - on Iyonix now coming to RPC soon).
Another point is a lot of code has been 32bitted, I know being a convinced Omega supporter you may not see the benefit in this - but there is.... let me expand, if you run 26bit code on an xScale (whenever that arrives) on the Omega (whenever that arrives) you'll have some sort of performance hit as the 26bit code has to go through ArmTwister - now if a lot of code is 32bitted - then it can run OPTIMALLY on the xScale on an Omega (so Omega users will benefit *because* of Iyonix).
The downside for Omega users is the "better than Iyonix" version of RISC OS is still just 26bit - and will ALL have to pass through ArmTwister (if an xScale is fitted). You'll have (depending on how MD implement it) either (a). the OS running at the speed of a 306MHz SA chip rather than a 1GHz xScale OR (b). at some performance faster than that but less than a flat out 1GHz xScale.
In short without a 32bit OS your Omega will *never* reach it's full speed potential.