Foster was part of the Birmingham team which won the League Cup two years ago with a shock win over Arsenal in the final.
But he admits the experience left the squad drained and Blues were relegated at the end of that season to the Championship.
Now Villa are just one step away from reaching the 2012-2013 final and are also embroiled in a fight to stay in the Barclays Premier League ahead of tomorrow's derby clash at the Hawthorns.
But Foster still expects them to go full throttle to triumph in Tuesday's Capital One Cup semi-final second leg tie against Bradford even though their 25-year stay in the top flight is in doubt.
Foster said: "The Carling Cup win took everything out of us at Blues. It was a huge drain on everyone.
"The next two, three, four matches after that final we were awful. We were as bad as I've seen us.
"It kind of snowballed from there. We had seven or eight games left and it was in our hands.
"I remember saying 'if we get relegated here, we only have ourselves to blame because we only needed four or five points to see us safe' and it never happened.
"It's mad to think that it could take weeks to get over something like that - but I swear to you it did."
Foster added: "People are saying Villa are in a similar position now but I still don't think they will change their tact.
"If they have a chance to win a first major trophy in a long while for the fans, they still wouldn't change it.
"They will still say 'let's try to win and see how we do afterwards.' You've got to do that.
"They are so close to the final now that they have to give everything against Bradford in the second leg just to get there. It's only one more game."
Foster concedes it would be a massive shock if Villa were to be relegated but also claims the big-spending approach of QPR in their current predicament represents a massive gamble.
He said: It's unthinkable. Villa are such a big club and the thought of them being in the Championship is crazy, when you think of the players they had a few few years ago.
"If you look at the teams at the bottom like QPR, they are spending a lot and chucking crazy money at it.
"It's great if it pays off and they manage to avoid relegation.
"But, if it doesn't, they are stuck with a huge bill on their hands and who am I to say whether that's right or wrong?"
The ray of hope Foster can offer to Villa is that they are still in strong contention to stay up and have not been cut adrift.
He said: "I was with Watford a few years ago years and we were in the relegation zone all the way along.
"The thing with that one was we were dead and buried by February or March.
"Villa are within touching distance now. It's a point in the season where, if you can string a few results together, you can climb right out of it.
"Something silly like two or three wins on the bounce gets you into mid-table. It's all to play for."