Let me pull a thenewgreen and give the questions some brief thought.

What do you guys think about marriage?

Marriage is a public affirmation of a private commitment. Even eloping, you still did the paperwork. Making it legal does not make it more sustainable or less sustainable; however if one of you previously expressed an ambivalence, getting married does send a clear message to the other partner. Marriage notwithstanding, having a committed life partner at some point in your life is a good idea, definitely something to try once or twice. Practice makes perfect.

Is it a silly cultural prescription?

Absolutely, luckily the "culture" is constantly changing and, while marriage used to be a form of slavery, it seems to be becoming (in some cultures) an egalitarian institution with many attempting it "in order to form a more perfect union" as Americans like to say.

Want a traditional reception and ceremony? Trying not to think about it?

Many factors will play into how you announce and celebrate your event. It makes no difference how big or how small the event is. The biggest weddings ever can lead to terrible marriages (Charles and Diana, for one).

Is it a super big deal?

I think having "a deal" is a good idea. My current husband and I made this deal: We'd stay together as long as the marriage was at least as interesting as our work -- or some similar silly thing. He's long forgotten what the deal was. What we needed at the time at our ages is definitely very different from what you need now. We understood that the other person was not there to make us happy. We are responsible for our own happiness and we are also interested in and committed to contributing to the other person's happiness -- but as I learned, I can't just be a candle in a dark place if the darkness can't perceive light.

ok, this is long enough.

Have a super happy life together. Partnering is a good thing and finding someone that you are looking for who is also looking for you is a miracle!