Depends on what you're happy with. If you and your fiancee ride a bike that looks like this and are happy with it, then the tandem is probably right for you. Don't worry about the bike being a few lbs heavier than a $4000 bike - the rider makes the difference not the bike. For example I used to knock out 57 minute 40km time trials on a 24lb road bike with downtube shifters that I wouldn't even look at today.
However if you ride what looks like a racing bike costing >$500 I would hold off until you can afford a new more roadie-type tandem like the KHS Milano. Quite a few people on the board here have got / had one and they are more than adequate for most uses. You don't need carbon dura everything to go racing, touring or anything else. It is nice but not necessary.