This is going to get long, so first question -- what convention? If it's Anime Boston, hecks yeah, just do it.
So your memory is pretty good. I know that we have talked conventions somewhere in one of the marketing threads or maybe it was the Dragoncon thread? (http://forums.webfictionguide.com/topic/dragoncon-should-we-go#post-9986). It's been a while and the search feature is not being all too friendly today. D<
I know that MCA Hogarth also tabled extensively last year as she tweets actively about it. She usually has the same tablemate and seems to be able to sell the books she brings. Based on my conversations with her tablemate (another artist I regularly chat with on social media), they mostly participate in the Florida convention scene. That con scene is a bit more "general"/"broad" than other conventions in the U.S. I know she posted a review of Megacon on her webpage but am not sure if the rest of her experiences are only caught via Twitter.
I have tabled in artist alley a few times here and there. (More times than I care to count UGH.) I'm less active than I used to be as they're pretty time consuming events.
However, unlike MCA, my main presence at these conventions is an artist. (Typical setup here https://twitter.com/whirlyshirly/status/310171364814376960/photo/1 )
FOr the most part my setup does not heavily advertise the serial. For most conventions until last year, I had only a bookmark on my table. Some conventions they go like hotcakes and others not so much but that's largely dependent on traffic flow and how people interact with the tables. Most people will never decline a free good quality bookmark. Mine are gloss on one side, heavy paper, and non-gloss on the side with text (Bookmark: http://t.co/AGOzTeDq3f ) .
I did have a few proofs at one convention last year that was oriented towards anime/gaming/comics. I sold and traded the five or so I brought with me ( Proof closeup here: http://t.co/4npONrXn. ). I simply stuck the proof out on the table (if you look at the picture above, it hangs out in the middle). The weird thing was people who like books will run over if they see them (they're so out of place otherwise). As I generally don't like to mislead people, I'm careful to first tell someone that the book is available online before proceeding with selling them the copy.
That said last fall I went to an anime convention and the book did not sell. Rather it drew other writers over to the table to talk to me. Some tried to recruit me for various fantasy/sci-fi cons in the area that are much smaller in scale in terms of attendance. I have not followed up on them as right now I still haven't finishe dthe proof and I would rather not go to any as a "writer" until the hardcopy of the book is done.
I have tried merchandise at these two conventions and others. Merchandise is also a crapshoot. One year, I sold a bunch of stickers and charms based off this design (http://t.co/2d75uq4X) but the market is saturated. People run away from the charms and buttons now. Stickers still go well but doing a reprint of the ones I have would be pretty costly (I got my initial set through a local connection). I won't be running any more for conventions. Still haven't tested their sale-ability online through a store. Unless you plan to be stuck with merchandise after one convention, don't invest a lot in making merchandise.
As for book sales overall -- I do talk to a few webcomickers online and at conventions when I see them. They do sell books but mileage varies depending on genre , display, and random things like how likable the people are at the table. Most do not rely on books alone. They have a mix of things from prints to t-shirts to buttons at their table.
My conclusion really is that conventions are always a crapshoot. They're risky for artists and vendors if they can't guess their audience tastes. They're going to be hard for writers perhaps unless they're friendly to webcomics. You obviously don't want to go to a convention where your stuff is totally mismatched with the taste of the attendees and you may wish to ask how webcomickers fare at the convention you're considering.
That said -- people have different goals in going to conventions. If you don't need to worry about making back cost and can stomach the idea of going to simply market, then it's worth thinking about. Hopefully the convention you're considering is local enough (or you have a free couch to crash on and low travel costs) so you can afford the gamble.
Make sure you have stuff to give away, most importantly -- business cards (if you don't want to do bookmarks) as people love to collect them.
And if you're going to have art prints, you will have to bite the bullet and look at something that is likely to bring people over. That usually translates to something fannish or something so witty or clever or cute that people will be drawn to your table.
There's not a lot of general advice threads on artist alley tables anymore out there on the internet as the population that tables has high turnover. Couple of places you could look up-
Facebook Group: Artists Alley Network International
Gaia Online AA thread: http://www.gaiaonline.com/forum/art-discussion/artists-alley-information-thread/t.21610915/
There you can get into more specifics on how to present, what sells, how many of "x" should you bring, etc. etc. You may also find people to hotel with and such in teh Facebook group.
Okay - this is far too long so I'll stop.