Helix was overbuilt from the beginning in the areas that mattered the most for future updating. The design goal was specifically to create a platform.
The technology is always less important than what you do with that technology. I have many digital devices from decades ago (e.g., Lexicon PCM-60) that use "antiquated" technology by today's standards. Yet they still sound as good as they did decades ago.
The main reason for wanting faster/more expensive/hotter-running DSP is to speed up the rate at which operations occur. If you find the latency in Helix unacceptable, then you may need a unit with more powerful DSP (of course, regardless of the DSP, there will always be the latency involved in A/D and D/A conversion). However, DSP alone isn't the only factor. The efficiency of the coding is crucial. Based on 3.50, it's pretty clear Line 6 has managed to increase the efficiency dramatically, or we wouldn't have better cabs that require significantly less DSP.
The question is simply whether Helix produces the sounds and effects you want. If not, then you need to find a unit that does. However, if you like a different unit better, it may have nothing to do with the underlying technology, but with the people who did the coding.