Do old sites with old content and old backlinks lose SERP value?

Will an old site that's high ranking eventually lose ranking in competitive niches if they do nothing and let it sit there, and it doesn't generate new backlinks? How easy is it to overtake these sites?

I know it should depend on the site, but is there any general trend?

Yes....you need fresh content and consistent, continuous backlinking to hold rank.

i think the most important thing is how often new content is added rather than new backlinks but i could be wrong.

I have a site that I haven't touched in almost a year... it's 45 pages deep a little over 2 years old has a lot of various back links (the majority articles) and is sitting on page 1 of google for a lot of different keyword phrases... some very competitive.

I stopped adding backlinks and updating it last September.

Google has it as a PR3 on the first page and many of the inner pages as PR2. When I did backlinks, I backlinked to all the inner pages as well as the first page.

It generates decent traffic and the revenue from it is in the 80.00 daily range using adsense and CJ.