First of all, thanks for the amazing work you have done with Limesurvey. I am a happy customer and I will be donating soon enough
Just wanted to share here how difficult / non-intuitive has been for me to find the Donate Link through the website and suggest that you place a link in the main website menu visible at all times (see for example the Libreoffice website).
Of course there are ways to find it (google it!), but I believe that a constant presence would help people keep in mind that Donations are important!