In my opinion it is not necessary. eBay capsules only let us to choose certain keywords, not specific products. Therefore it updates automatically each time a featured/most relevant product on your capsule is deleted/not listed anymore.
As maybe you already know, there were almost 2 whole years when I was kinda 'away' from HubPages. During this time I payed no attention to my hubs/capsules/account/anything at all and still, my capsules are still working.
On the other hand, Amazon capsules are different - in case you choose products on your own and don't let the capsule choose the most relevant products according to the keyword(s) given. These may require update more often, because once the product is gone, you have to select a new one. According to my experience, these are also very rare, so basically it is enough to re-select some products once you feel like there is a new one that might be even more relevant to your hub.
Happy hubbing! :)