Rooney has missed the Toffees' last two matches after picking up a virus before Christmas while McCarthy has only featured once this season, with knee and hamstring problems blighting his campaign.
Allardyce has spoken frequently about Everton's lengthy injury list in recent weeks and is understandably about happy about the returns of Rooney and McCarthy. The former England manager will also be able to utilise the talents of Yannick Bolasie, who came through his return to first-team action against West Bromwich Albion unscathed.
"Wayne's better, any quality player that gets fit will be a big boost," Allardyce said in his press conference. "McCarthy is out training with us and should be fit for selection now.
"I think a lot of players have been out for far too long. Some have been inconsistent and because of that inconsistency all we've done so far is transform the team defensively, that gives us a good platform for a results."
The returns of Rooney and McCarthy are timely boosts for Everton, who lost Idrissa Gueye to injury against Chelsea last week. The Senegal international looked primed to miss a substantial period of time with what looked like a nasty hamstring problem, but Allardyce believes the combative midfielder could return for his side's clash against Manchester United on New Year's Day, though he was less positive about Leighton Baines' fitness.
Asked about Gueye's availability, Allardyce said: "We will find out this morning. Might be risky for tomorrow, we're hoping he will be okay for United.
"Yannick seems okay, but you can't play them all together. Wayne's been in bed for three or four days, James has not played for a while. It will be good to have them back in the squad.
"Leighton's calf is still a concern. We expected him to be back in full training next week, but that will not be the case now because he's had a setback in his rehab."
Allardyce later turned his attention to two of Everton's long-term injury victims. Seamus Coleman and Ross Barkley have been sidelined for nine and six months respectively, but the pair are recovering well ahead of the business end of the campaign.
"[Seamus] is coming on okay," Allardyce said. "He's out running, not doing any more than that at the moment, he's progressing nicely. We've got a new machine in so he's a bit of a guinea pig on that, we'll test it on a few more players in the next week or two.
"[Ross] is training with us. I think at some stage the medical staff will say you can have him. I'd have liked him two weeks ago but he's training with us on a regular basis and is very close to being available."