The Lions crossed for 10 tries in Johannesburg as they ran riot against the Golden Lions and then non-plussed the Free State Cheetahs in the opening quarter with a point-a-minute blitz that eventually enabled them to win 26-24.
"We've been to Bloemfontein a couple of times and come off second best. For the Lions to go up there and get into a 20-point lead was a very special effort," said Plumtree.
"If they play the type of rugby they did in those first 20 minutes then they are capable of putting away any team. They are a really dangerous side when they get quick ball and dominate the tackle area.
"Their performance against the Golden Lions was pretty outstanding as well. Every time you go to Ellis Park you get a difficult game.
"If they can do that to them there, then they have to be rated. This is a much stronger side than they had in New Zealand.
"It is better organised and there is more competition for places in the Test team. In 2005 the tour was dominated by Englishmen and they dominated the team selection.
"But if the Lions are going to win one it is going to be the test in Durban. That's going to be crucial for them because it is so much harder on the High Veld."
Plumtree coached the Wellington side that faced the Lions in 2005 and just missed out on playing against the tourists for the Natal Sharks in 1997. Injury problems forced him out of that game and the following week he headed to Wales to take over the coaching reins at Swansea.
His Sharks side that faced the Lions on Wednesday, June 10 were robbed of nine players who were involved in the Springboks squad and he believes there should be a different emphasis on the Lions tours.
"It is a pity we don't play full-strength sides against the Lions. It's great for us as a province to have so many players in the Springboks squad, but Lions tours are quite unique," he added.
"My players are talking about the game and looking forward to it, but there isn't the same cache as there used to be. They're looking around the names of the Lions players and don't know many of them.
"I don't think there should be the same pressure on the Springbok management to beat the Lions. They should be more focussed on winning the Tri Nations and using this tour to help them achieve that.
"A Lions tour should be a celebration of rugby. I'm a bit of a rugby romantic and I remember the days when the Lions came over to New Zealand and had to play a full strength Auckland side and other provinces with all their top players.
"That certainly made the tour much tougher for the Lions and worthwhile for the players and fans. I would just like to see the emphasis change a bit."