Well, changing from drop to flat bars usually requires changing brake
levers and possibly shift levers. Maybe cables as well. It's kind of a
pain, and maybe expensive.
Have you considered just installing a much taller stem and keeping your
current handlebars? Some people say if you rarely use the drops, your
bars are probably just too low.
Most of the "bike fit" rules of thumb seem to recommend having the tops
of drop bars level with the saddle, or maybe an inch lower. I see no
reason not to have them as high as you like. You can then ride with your
hands on the tops most of the time, but still have the other hand
positions available - for example, for climbing hills or grinding into
headwinds.
--
- Frank Krygowski