Welcome to TIG brbehl
I bought my Glasslite X-Wing a few years back when prices were normal for around 100 Euros. Sadly I had to move it on for financial reasons last year and I got 270 Euros for it on eBay with several bidders interested.
The Caça Asa X is a beautiful and unique X-Wing, and my version was pristine and boxed, but with no insert or instruction sheet or transfer sheet. The wing opening function on mine was also faulty and only opened partially.
Yours should fetch a premium because you have the insert and two sheets. However there is some discolouration to the chassis underside and a wing of your vehicle which will detract a little from the price.
Try searching eBay complete listings and ask around any specialist Facebook groups for current prices.
When I sold mine I started it at around 100 Euros the price I paid and let it bid up. Pics of mine on my guide here: http://www.imperialgunneryforum.com/t7463-the-x-wing-fighter-variations-thread#Glasslite
thevintagetoyadvertiser.org 1970s and 80s vintage toy ads and other retro paperworks
imperialgunnery.com Vintage Star Wars action figure weapons and accessories guide