Depends on why your building the model.
In General
1. If it's just for fun add as much or little as much detail as you want.
2. If the area will be sealed up and not visible there really isn't much reason to add the detail unless it just makes you "feel" good.
Contest Modeling
If the model is for a medal or open judging type of show extra detail is usually a good thing. If the model is for an IPMS sponsored show the detail will only matter if the basic construction is good. Most of the time at IPMS shows your better off with a stock out of the box model with top notch basic construction (no seams, no punch marks, no glue spots etc) and no extra detail than lot's of details added and an unfilled punch mark or seam.
Poorly, excuted detail like mangled photo-etch, resin with tool marks, crooked parts alignment will actually hurt the model at a show that places emphasis on clean basic construction ie the typical IPMS show. Adding detail can be an opportunity to "mess up" in some cases.
Personally, if the model isn't a contest model, I'll add detail until I get bored and want to move the next project. If the model is a contest model, I'll only add stuff I know I can do and get right. Most of the time I build out of the box kit's because I enjoy building and painting more than detailing. Painting and weathering is the most fun part of the hobby for me.
The Cat's Meow
Scratchbuilt when done correctly trumphs aftermarket details and resin, in the wow factor and contest circut. My skills are very lacking in this area but I have the greatest respect for those that can do it well.