We went through an elevator replacement about 7 years ago. Our building is 8 stories with just the one elevator, so accessibility for shareholders on the upper floors was a factor. Here are some of the lessons we learned from the replacement experience:
* I think all elevator replacements today incorporate sophisticated computer circuitry to enable convenience and safety features. These controllers are not as rugged as the old relay banks. The room that houses the computerized controllers will need to be environmentally controlled (temperature and humidity) and the power to the circuitry should be filtered and regulated. A failure in the computer will almost always cause the elevator to stop. This is something you don't want to happen when there are people on board.
* The parts being replaced, especially if they are very old, can have high value on the resale market. Don't just let your renovation company cart them away. See if you can get an appraisal and then try to negotiate a price decrease with your renovation company. A Google search on the internet would be a good place to start.
* To help our shareholders who lived on the upper floors move packages up and down, we hired a full time porter during the months the elevator was out of commission. Our renovation took place over the summer, so we hired students who wanted to earn the extra $$$. The summer had its drawbacks because stairwells are not usually air conditioned. We ultimately had to install a large through-the-wall unit to prevent heat-related problems.
* Pre-planning as much as possible before the elevator was taken offline, and keeping the shareholders as informed and up-to-date as possible was key to keeping aggravation to a minimum. No one enjoyed having to trek up and down flights of stairs, but as long as people knew how things were going and when they could expect elevator service to return, they accepted the aggravation gracefully. One happy benefit from the elevator being offline was that we had a much more fit community at the end of the renovation.

Good luck with your project if you decide to renovate.