Both men have been a hit at Ewood Park after arriving for paltry fees with Samba, 25, now valued at many times his £400,000 transfer from Hertha Berlin in January 2007.
"The big man's been brilliant since he's been here," said Nelsen. "He came for nothing and has provided some fantastic service and some quality performances.
"In the long-term it bodes well for Blackburn's future."
Interest in Samba from teams competing for places in the Champions League would not surprise Nelsen.
"It is up to Chris how far he goes," Nelsen said. "He has all the qualities: height, speed, technique, all that.
"When you have all the attributes it is up to the individual. "If he keeps performing with Blackburn things will happen but I am glad he has signed here."
Sam Allardyce, who returns to old club Bolton on Sunday seeking to avert an 11th straight Premier League away defeat, said: "The core strength of your side lies down the middle: your goalkeeper, your centre-halves, your midfield and forwards.
"You build the rest of your side around that and Chris' experience in the Premier League is invaluable to us as a team. "At his young age it is securing a valuable asset as well as a very good Premier League player. We are all delighted he has signed a longer-term contract."
Blackburn have already secured local bragging rights over Burnley but a second victory over Lancashire rivals in quick succession would halt an alarming sequence on the road.
Although they have visited Arsenal and Chelsea twice since mid-March, and also played Manchester United and Liverpool, their appalling recent away record of four goals scored and 32 conceded in 10 league matches threatens to drag them into another relegation scrap.
"We are obviously going for a win but anything away from home at the moment would be a positive," said Nelsen. "We need to end it and end it quickly. "There have been some pretty tough away games but we have looked at what we can do to remedy the situation. Hopefully we can put it to bed and get on with the season."