What Tim said.
I'll be getting at least one of each Egyptian set, but probably waiting until they're available in the UK shops, unless I get jittery and buy from a UK seller I know who gets them early at about 10% about RRP. If they're not good value for money, I'll probably only be buying one though, not several of each.
When they are officially released in the UK, I'll be checking the 4-5 Brick and Mortar shops I can reach (TRU, John Lewis, Hamleys, Bentalls, and a small independent) for the best price, which will probably be John Lewis, plus the Playmobil UK site. At present the Roman Arena is £50 in John Lewis, £60 on Playmobil's website, and £75 in the small independent toystore, so it's well worth my shopping around.
In the case of the Egyptians, I'm not worried that they'll never appear in the UK and I'll miss them. In the case of some other sets like the 4444 Pinnace, it was labelled as a limited edition, I wasn't sure how limited, so I got mine from a friend in Germany just to make sure I didn't miss out, or get ripped off on eBay.
The 5827 Roman Blister pack of all the recent releases is the one I'm most interested in right now, and I'm going to want about 24 of them because they'll form army units, so it makes sense that if I can shave $1 off the price I'm going to, but not at the risk of not getting them at all. I'm reasonably sure they'll appear on the Playmobil UK site some time in the next six months, so I'm happy to wait, or get them in the US when I visit, which would be much cheaper.
The point I felt you missed is that it's possible to consider a set poor value-for-money, but still buy it.