You are right about the capacitor ripple current rating, it is simply based on dissipation (Irms^2*ESR) and can size, for a given temperature rise (usually 10°C or 20°C). But the rating applies to caps at maximum rated temperature, say 85 or 105°C. If your ambient is lower than that, you can increase the ripple current.
As for the life of the cap, the number of hours given in the datasheet (1000~7000) this refers to the cap again at the rated temperature. But each 10°C difference results in doubling the life of the cap, so life should not be a problem. But if you want, you can "cook" the caps.
In other words, if you have to, you can increase the ripple until the cap reaches 85°C at your maximum ambient and you will still get 1000 h of operation (crude approximation)
This approach would allow you to use fewer capacitors, in order to save space.
One other thing you should be careful about is the high charge/ discharge current, not just the ripple. So you may want to consider caps that are specifically designed for high charge/ discharge currents. Typical caps like these are those used in flashes, where the high discharge currents occur. Series QS caps from Nichicon, for example, are adequate. The trouble with these is that they are necessarily high voltage caps and so they come in low capacitances and large cans.
Try to see if other manufacturers rate their caps for high charge/discharge currents, as this seems to me an important point. That is because the internal contacts may not take the high inrush current, even though they can easily handle the RMS. I would pay special attention to this.
For more info, see this article, too.
www.kemet.com/kemet/web/homepage/kfbk3.nsf/vaFeedbackFAQ/D68F1B97FC4FE31385256F72006669BD/$file/Technical%20Update%20-%20Ripple%20Current%20Capabilities.pdf