A lot of time can be invested in creating an improvement plan. If you subscribe to the PDCA (Plan Do Check Act) approach to continuous improvement then I am sure that you will too.
There is a drawback to the planning stage however.
There will be certain things that you can only find out, and learn, by undertaking the doing part (the D in PDCA).
The more experienced you get at planning the better your plans will be. There are also other things you can do to improve the quality of your planning (by using the FMEA approach for example), but fundamentally the reason that the continuous improvement cycle is a cycle is that you will gain additional information each time you attempt the improvement.
If you feel that you are getting stuck at the planning stage then it may just be time to get into the doing phase and see what happens.
Author of 'Business Process Re-Engineering', a practical plan to improve business performance.