The investment you make in remodeling your bathroom could return some of that cost. The Remodeling magazine has statistics for the United States based upon location and type of remodeling project.
With regard to any kind of electrical or heating work, please consider hiring a licensed professional as these types of upgrades need to be done correctly the first time, so that they are safe and problem free. Ripping-up tiles to get at the sub-floor heating underneath, and then repairing the problem by installing new tiles, can become a costly operation. Get a written warranty from a company on any damages resulting from their work.
If your hanging lights are dated, the options for updating them are endless, because hanging light fixtures can be replaced for about $25.00 on the low end. But if the fixtures are in good shape, you can easily just replace the glass globes on your hanging lights for about 5 to 10 dollars each. Or, you can get globes in decorative art glass and spend a little bit more.
However, if you follow the few simple pointers mentioned above and make a good job of it, making great looking shelves from old laminated chipboard furniture is a quick and easy DIY task; and at the very least will make a good semi-permanent solution to your shelving needs until such time as you have the time and money to remodel your shelves using real wood.
The showerhead will probably unscrew from the shower arm without the need for a lot of force. But sometimes the old showerhead has been in there a long time, and it can be pretty tightly stuck on by accumulated corrosion and other mysterious gunk. (Not unlike one of the lug nuts on your car.) If your showerhead is stubborn about coming off, use a pipe wrench or other wrench to unscrew it. As a last resort, apply WD-40, wait a few minutes, and try again.