One of the flattest collecting areas for many years has been the pre-1896 items, especially ribbons and tokens. Data from Hake's Encyclopedia of Political Buttons updates confirms these trends. Hake's updates show the least appreciation for early items. Items have upward and downward trends not only by era and candidate, but also by medium. Pinback buttons remain the favorite, especially jugates, followed by single picture buttons.
Cellos tend to be favored over lithos, and lithos over tabs.
Studs and ribbons lag a bit behind the buttons, with paper items behind that. Of course a graphic and colorful poster may excite a lot of interest, but only the truly historically-minded collector will spend much money on an unillustrated pamphlet. Many a savvy collector has a lot of fun, and builds a strong collection relatively easily and cheaply, by specializing in things other collectors bypass. Some of these areas might include 20th century jewelry, bumper stickers, or 19th century copper tokens. I once heard a coin dealer advise a beginner not to think of his collection as an investment.