Sorry Coccinelle, Whoever told you that they gave bubbly if you said it was your first flight was talking b'locks.
I worked on checkin for a very reputable full service airline, and never once did that happen based on what a checkin agent said..
Very occassionally we will upgrade someone on honeymoon, or on their birthday or anniversary, but only if the airline actually needs to upgrade someone anyway (i.e there arent enough seats on economy) and are looking for who to do it to, and it says "honeymoon" etc in the system.
But bear in mind, the checkin agent gets people asking for upgrades for some reason or the other, ALL the time Honeymoon, birthday, broken leg, feeling sick, funeral,bad back, important work trip, cold, anniversary, you name it, they have heard it (and so did i!), so if they really did give out booze and upgrades on demand, then all the airlines would have club cabins full of upgradees and would have been bust for years! And when you have been asked for a free u/g for the 20th time in one day, really, its very annoying, and most likely to have the opposite effect!
Best thing with airlines, is be really nice and chatty to the agent, and CASUALLY drop in the fact that its your birthday, honeymoon etc, i.e. we are so excited about this trip, its our honeymoon and we've never been to Bali before... And DONT mention an upgrade at all. It might work, or it might not, but its more likely than a blatant blag!
Hotels are different, i have been given a bottle of wine and/or a cake several times when away celebrating birthdays, whe they have seen the birthday in one or other of mine or OHs passport, or if i emailed ahead to tell them.