Then don't grind on the characters you don't want to grind with anyway? You can grind them on your favourite character and simply transfer the item you purchase in the end. If the helix-components were going to be Legacy bound, you'd only get an incentive to start grinding with the characters you don't want to grind with, to get them faster. It works EXACTLY the opposite way from what you're afraid of.
You're right I don't grind on all my toons, but I do use all my toons and play them all for raids/pvp/etc. Just by doing xeno and the other worlds bosses i can get quite a few grey helix's per week. I do however mainly grind on one toon, but the legacy bound would still help.