Collecting smoking pipes is a fine old hobby… the older the pipes, the finer the hobby. When philately was young, it was ancient.
The requirements are near to non-existent: own more than one pipe. Smoking them is optional; owning them is enough, though owning and smoking them is best. And the agglomeration need not be out-sized, or costly: though hand-worked meerschaum may command hundreds of dollars in shops, an elementary briar is nothing to sneer at.
One benefit of collecting pipes, instead of other ephemera, is that pipes remain useful once collected. Unlike postage (once you use a stamp – that is, lick it and attach it to a letter – it leaves your assemblage, likely for good), pipes can be used and re-used, yet the collection remain whole. Indeed, use can even improve the timbre of the cache considerably. There is no interest in new pipes, save the interest of breaking them in. The stories belong to older pieces.
Most pipe smokers turn collectors, though not by intent: they begin with one pipe, add a second, and two quickly becomes five. The scale is manageable, but the collection is born. Collecting pipes is a natural, pleasurable consequence of smoking them. True, not every pipe can be smoked; some are too old, too dry, too fragile. Those tend to be too expensive, also, for the tyro. For collectors of means, however, pipes fall within one of two categories: those collected for beauty, history or value, and those collected for smoking.
Per the costlier specimens, time is money: the older the pipe, the more murderous to bank balances. Still, meerschaums with forty or fifty years’ history on them can be had reasonably at most antique and curio shops, in addition to the porcelain pipes so popular in central Europe a century ago.
This is not to discourage the purchase of new pipes: collectors on the make should purchase whatever modern pipes suit their tastes and budget. They can be smoked regularly, not just admired, and such interaction with pieces of the collection will increase the pleasure of collecting itself. Afterall, everything new will one day be old. It will have its own history. In terms of your pipes, their history might as well be yours.