Doyle cost £6.5million when moving from Reading in the summer but McCarthy believes he has already been worth "every penny" with his contribution to Wolves' bid to stay in the top flight.
He has scored six goals and in recent games has led the attack effectively in a revamped 4-5-1 formation which has helped Wolves to earn a draw with Liverpool and a win over Tottenham, lifting them out of the bottom three.
McCarthy said: "I'd hate to put a value on Kevin. He is a very, very good Premier League player.
"He is playing for a team scrapping at the bottom, he has scored his six goals, he has caused everyone he has played against problems.
"He started off with a hernia when he came here so he got off to a slow start, missed games, then came back and wasn't fully fit.
"But since he has got fit, he has proved to be the player he was two or three years ago in the Premier League when he scored 12-14 goals.
"Does he look a bargain? I will accept that. Whatever we have paid for him, he has proved to be worth every penny."
When asked if Doyle could become a target for clubs this summer, McCarthy admitted: "Look, when someone plays well, that goes with the territory.
"I never lose any sleep about anything like that, because I can't do anything about it.
"It doesn't concern me at all. Doyley came here and is loving it and, if we stay up, we are a Premier League club and he would still be loving it.
"But if someone like a Manchester United come in and ask and offer, it is bloody hard work then isn't it?
"If we stay up, have a good finish, and we are comfortable, then we go and ask about someone because we have got money to spend.
"That just makes the world go around so it doesn't worry me. If we stay up, I'll be doing it to someone else."
McCarthy is unsurprised Doyle has made such an effective switch from operating in a 4-4-2 formation to his current role as the sole forward player.
He said: "Kevin is relishing it. He has played the role before. He has a very good understanding of it. He loves it. He is up against two centre-halfs, occupies them for most of the game.
"He has given everyone problems - and he will give these two problems on Saturday against Chelsea.
"I think he has got better. I thought he was a top-drawer signing or I wouldn't have paid what I paid for him when I went out and did it.
"He was the first one, I wanted to sign him, and I've been thrilled with him. He murdered us here when at Reading last season. He ran us ragged when they beat us 3-0."
McCarthy has already named the side which overcame Spurs to face the league leaders and insists recent performances give him cause for optimism.
He said: "I don't think the game has a fear factor because we have been playing well. I don't think it is about the level of the opposition that is coming. They are arguably the best in the league this season.
"I believe it is all about how your own team are playing that gives you confidence. It is how we have been playing that gives me confidence.
"We deserved to win. We played well. We didn't have that many attempts on goal but it was a solid performance.
"The team that will be playing is the one that played against Spurs. They all deserve to play again."
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