I'm probably going to catch heck for saying this but I just did the same thing. I had 3 goldfish in a 10 gallon tank and just upgraded last night to a 29 gallon, and I was told use everything out of the 10 gallon, filters and all. My only problem is that I have to re-cycle it again. My nitrite levels are to high.
But I have taken notice just since I did that my fish swim around more, and they just look healthier.
I reused the gravel, filters, bubble wall, plants and whatever else was in there.