The "provisional" approach does have time limits and may cost more in the end.
Another approach is to very carefully document your meetings, discussions, research while you develope or refine your concept and determine the market value and customers. - Anyone can get a patent, but unless you can market it or find a solid partner, you are on an ego trip.
Talk about your initial concept (Phase I) while you are developing the concept of the finished concept. Doing this, any copiers or others that sense a development in a an industry will be looking at the old research, while you are devoping the Phase II, III or IV, which can be shown to be the most recent. - This will give you additional credence to your application.
If you are fortunate enough to get a valuable patent, you will have to be able to defend it against the copiers. Since you have the documented research, meeting notes, comments and contempranious notes, you should easily be able to defend it against the people that copied Phases I if you or your partner have the resources to stop the pirates.
The last patent suit I was involved in had over $760,000 on one side invested in legal fees before I was called a year ago.