In my opinion, I don't feel bored to collect safety cards, I collect safety cards more than 4 years, I have almost 1100 safety cards, I think collect safety cards just like collect stamps or telephone cards, have to spend long time to collect. If all the cards are send direct from airlines, it is easy and bored, and this is not a hobby, hobby is that you try to find to buy/trade by yourseld, I think always need try to find in the airliners show, eBay, other collector trade list to find your favourite card is much happier than just get idirect from airlines. Like me, when I started to collect safety card, I want Dragonair B737 safety card, I just find it and bought it a week ago, for now, the value of the card is not important for me, but that can show the how am I work-hard to find the card.
Also, collect safety cards can help me keep close to airlines news, like they change new logo, fleet phased out, fleet development..... That is a chain, if I don't collect safety cards, I never that know much of airlines news.
Of course, eBay some of time sold card in around $10 each in common card, but how about the old cards? I don't think that expensive to buy a 1970s-80s in around $15 each, at least eBay is a good source for me to buy some un-popular cards.
By the way, in my opinion, collect everything need time, IF you really enjoy to collect, you never feel bored!
Seriously, if you don't want your cards anymore, just sell them in around $2-3 each, don't sell in eBay for $10 each!