Your observation about that lefthand promo rail is correct -- most papers that tried it have jettisoned it (or desperately want to). The problems outweight the benefits, the problems being:
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—-- if the rail is wide enough to be effective, it gets in the way of the layout and seriously reduces your full-page design options;
— no matter how wide it is, the promo rail can't accommodate big or wide images; and
— it turns into wallpaper very quickly, which means it can easily become invisible to the reader. (That’s the main reason we killed the Page One rail years ago at The Oregonian, at right — it became unredeemably stale after just a few months. Also, the publisher had this thing for yellow, even though the entire newsroom found it gagworthy.)
Yes, if you want effective promos, you pretty much need to run them horizontally. That way, you can vary the number (say, from one huge promo to maybe 3 or 4 on any given day). You can vary the promo headline treatments. You can use type only, or cutouts, or — well, you get the point.
Variety is key; if you don't keep them fresh, they'll quickly turn back into wallpaper. (Or to put it another way: If you don’t care about your promos, your readers won’t, either.)
As for top vs. bottom, the thinking now seems to be: are you trying to sell papers, or just get the reader excited about what's inside? Unless you're in a competitive market battling it out at the newsstand, forget about using promos to sell papers. They won't. Only huge, loud and sexy promos sell papers, and those may be massive space-wasters for you. Instead, think of promos as a sort of super-index. And if you run them at the bottom of the page, readers can see them just fine. You can even vary the depth from issue to issue, if you want to.
I'd vote, above all, for maximum flexibility in promos. Keep them surprising, keep them lively, and keep the images appealing.