Friend (32m) still owes me (33m) an unpaid debt, what to do about wedding gift?

For as long as I can remember, I've been best friends with four guys, we'll call them Ron, Sam and Dave. We've grown up together since elementary school and have shared a ton of crazy adventures together.

One thing we started doing after college was taking international vacations together, we toured Europe, SE Asia and a few other spots. About 5 years ago (2012) we decided to do a big "blow out" trip. We spent 2.5 weeks traveling around South America. Now, Ron and Dave have normal office jobs and Sam is a public school teacher. I am by far the wealthiest of the group as I'm a corporate lawyer at prominent law firm in a big city. As one may imagine, Sam could not really afford the trip at the time, but it was his DREAM (the #1 place he wanted to see before he died was Macchu Picchu, he talked about it all the time). But Sam is one of my best friends in the whole world, and I didn't want him to have to miss out on something he had dreamed about his whole life, especially because these trips had kind of become "our thing". So, I told Sam I'd help cover his trip and he could just pay me back as he was able (i KNOW... don't lend people you know money if you need it back). In total, I loaned him about $5k.

It is now 2017, and while Sam has paid SOME of it back, most of the balance is outstanding (currently around $4k). I'm fairly wealthy, and to be honest, if Sam never paid the debt back it would probably not really have any affect on me. As such, I haven't really pestered him about it.

My dilemma is that Sam is about to get married. I'm am an etiquette guy, and as such, if I go to a wedding, I am ALWAYS bringing a gift, and if you're a close friend like (Sam) I am probably giving you an expensive one. Dave and Ron previously got married and I both them both expensive gifts ($500+), and Sam knows exactly what I got them. I'm a bit torn between my inclination towards "etiquette" and my feeling that I shouldn't be giving someone who has owed me a $4k debt for 5 years an expensive gift. I know I definitely don't "owe" him a gift, I just feel like a bad guest if I show up empty handed, and I want to make sure Sam knows that I am truly happy for him and want to celebrate his wedding. I'm worried he would be especially hurt knowing what I had previously got Ron and Dave. Am I being crazy?

TL;DR I lent a close friend a large sum of money for a trip 5 years ago. Debt never paid back. What do about a gift for his wedding?