You have to weigh cost versus benefit. You don't provide enough information about your project to allow us to advice you here, but consider:
- cost of conversion is pretty small. C# 3.0 is almost completely backwardly compatible with 2.0 and run on framework 2.0
- benefit is also pretty small if the coding is almost finished, but might grow in the long run. A new feature you might have to implement in the future might turn out to be much easier implemented using Linq, for example.
