Is it a good idea to install gedit in Lubuntu?

None of the packages on that list will load anything that can make your system slow down.

It will install the necessary libraries, the rest of the dependencies that are not satisfied, etc but will only call them when you run gedit and will go away when you close it. I dont think you will have any performance issues related to installing gedit on your Lunbuntu system.

gedit installs GTK+ libraries - GTK+ is already in use in parts of Lubuntu.

For example - the default editor leafpad is a GTK+ application.

No real Gnome dependencies are actually installed that you really dont want in LXDE such as gnome-panel. Thus - dont expect any adverse "performance" issues when using gedit.