Improving a home's energy efficiency is a common sense undertaking, but it's worth considering when you actually do it. The first thing to bear in mind is that the existing building stock is not static, it's in a life cycle. Eventually all houses will need some maintenance, whether it's new windows or getting the roof fixed etc. We have to realise that this is the very moment to improve insulation and so on, otherwise it's too expensive. If the scaffolding is going up anyway then take advantage.
Also, when you upgrade a component you should go for the best available because it could be 30, 40 or 50 years before somebody needs to do the job again. The key here is not to do a job just to save the energy, as the cost will be considerably more.