If you want an accurate Appraisal, you will probably have to disclose some information about your income as most people value sites based on income.
Regarding how you can improve your forum, feel free to request a review. One thing might be to get a custom or premium theme rather than use the default Xenforo theme.
It's been a couple weeks since you last posted about this. Master A is right you will have to disclose a little more information in order for us to give you an accurate appraisal. The Community Reviews section is fantastic for detailed critique if that is what you're looking for. If you're needing an activity boost the Posting Packages area is the place to be. 🙂
Hi! Your site at the moment seems dated, which shouldn't surprise you as you have said that it has been going for 10 years.
What I would suggest is that you have a look at sites that inspire you, it doesn't have to be sites like yours but websites that you look at and go wow too. next take a notepad and write down all the features you like on those sites and you will basically be generating your own checklist.
The next stage will be to look at flat and on trend designs. Places like Awwwards.org are good places to look first. The trend for the moment is flat design or flat shadow design.
In the case of your forum try looking at the theme of your site in order to best design the layout and whether you should feature images one your site rather than text links for forum boards.
one of the best tips I can say is, simplify your logo and work on the text (fonts {typefaces} ) you use.