Are you based in Australia? If so, then it can be a little more tricky to earn Aeroplan points. There is a
Star Alliance credit card from HSBC that lets you accrue Aeroplan points at a rate of 0.8 points per $ spent on the card. In addition, this card will enable you to earn Star Alliance Gold elite status with Aeroplan after spending $4,000 within the first 90 days of opening the card. This would provide you with additional checked bags, lounge access, priority everything to name but a few items when travelling on any Star Alliance airline (e.g., United, Singapore, Air Canada, Lufthansa, Air New Zealand, etc.) Aside from credit cards there are a number of
partner airlines in the region that let you accrue flights to Aeroplan. In particular, Virgin Australia where you'll earn 50% of miles flown as Aeroplan points when booking a Choice fare (or 100% on Flex, 125%-150% in business).
If you're outside of Australia, there are better credit card offers. For instance, Aeroplan is a transfer partner for Canadian and US American Express cards which transfer over at a 1 to 1 rate.
In general the best time to buy Aeroplan points is when they have bonus points offers in the 80%+ range. I've done this a number of times now and have managed to fly Sydney to Toronto return in business class for roughly $3000 CAD all-in. The key when buying any points is to ensure you have an award booking with availability ready to book once the miles are transferred over (and ideally a backup option should that one disappear).
-RooFlyer88