Ashes are a symbol of repentance and man's (or woman's) humble place in the universe and thus inappropriate for a Sunday Eucharist, which is always to some extent symbolic of new life and the resurrection (That's why Christians meet on the first day of the week instead of the last day of the week- a custom that is so old it's mentioned in the bible).
Now, of course, Sundays in Lent are a bit tricky because you've got a symbolically "happy" day in a symbolically "somber" season. They suppress the Gloria, use of Alleluia, etc within the Eucharistic service and whatnot to maintain the appropriate seasonal tone. But, still, imposing ashes on a Sunday would be a little much.
Stick with Ash Wednesday on a Wednesday. I mean, Wednesday is right in the name.
I'm also one who thinks that things like Candlemas, Ascension Thursday, Epiphany, etc. should do done on their actual days and not skipped or transferred to a Sunday, but then again, I don't have to deal with the fact that about five people would show up and I probably wouldn't even be one of them.
Priests and vestries have to keep certain practical logistical concern in mind that I don't have to, so it's easy for me to say whatever, but perhaps not as easy for them to actually *do* whatever.
Granted, I'm not really attending any church in any communion regularly these days (Hopefully I can say that without the CF police conking me over the head and banning me from substantive discussion on these forums like they sometimes did to people in the old days- I've heard things have changed a lot since then). A good Candlemas on February 2nd in the evening somewhere within a half hour's drive probably would have gotten me into a pew somewhere, though.
I think clergy sometimes underestimate the appeal of special events to irregular church goers. Candlemas was always my favorite feast day- a decade or so ago I used to drive an hour or two each way just to attend a Candlemas service 2 or 3 years in a row (Maybe non-consecutive years). But Ash Wednesday is maybe a better example in general non-me terms of a huge, huge thing, probably third only to Christmas and Easter, as far as bringing out people who normally don't come out. Sounds odd for a somber commemoration in the middle of the week that doesn't coincide with secular celebrations, but people want those ashes.
I think there are things on the calendar that could built into "the next Ash Wednesday" with concerted effort.
