IMO there is a point of diminishing returns for citation building. You can claim the big ones that get traffic, but end up spending more time on the smaller more obscure ones. We (HubShout) ended up going with Yext for the citation portion of our plans. Colan's MozLocal suggestion is another one we've used in the past. The biggest thing is to make sure you're spending the time where it's most needed. If the client really has a crappy citation profile, then maybe it's worth it. Most sites take a while to update the listings anyway, so finding a less-manual solution is ideal. All depends on what your clients need, and what kind of results you can deliver overall (consistency is key to citations).
Like Colan mentioned, you just need to find a routine that works well for your clients and then stick with it. Have a script/instructions ready so you can walk them through the process and keep them informed on what's going to happen next. Do it in chunks so you're not tying up the phones all day. Also warn them of the up-sell attempts - Citysearch automatically directs you to their sales team FYI.