I think you could really extend playtime by increasing the amount of wood needed for foundations to increase the value for raft pieces and change the way items spawn so there are random clusters of items and periods of time when there wont be any items drifting in (although it would be best to have the first wave of items set so there are not many bad starts). With this it may also be better to increase the yields from barrels along with adding the materials you can get from taking the barrel itself apart.