For me, it depends.
'Intent' is what gets us shot in the foot.
We end up with shit like 'constructive' intent.
Possession with 'intent' to sell.
The law likes to make broad assumptions as to one's intent. When many times, the law doesn't know shit.
It should not be illegal to plan a murder, and there should be no punishment for it, right up until the time that I actually move to commit that murder, or pay someone to do it, etc., and cement my 'intent' into place. I can fully intend to kill my ex, right up until the time I sit parked in her driveway for ten minutes, and finally decide that the bitch isn't worth the hassle. When I leave, there is no harm done.
Same with a robbery. There should be no crime, and no punishment, right up until the time I step through the bank doors and demand money. If I get cold feet in the parking lot and leave, I have done nothing wrong to anybody.
'Intent' and 'in the commission of' are two different things, and should be dealt with differently under the law. Often, they aren't. The law gets to assume an intent, and punish based upon that intent, resulting in the myriad victimless crime laws on the books in this country. To bend a fun phrase, you can intend in one hand, and shit in the other, and we'll all see what gets you a faster end result.
So yes, an attempted crime that fails due to poor planning or outside intervention should carry the same punishment, if that crime is actually in progress and you are thwarted 'in the commission of' that crime.
Intent however is a slippery slope, and is better left judged only in concert with concrete action.