Those Biplant offerings look nice, Rupert, though I'd guess they'll have historians rending their tweed jackets in horror.
As for me, I've nearly completed my collection to be used in a fictional El Dorado campaign. Years ago Chris Peers wrote an article in Wargames Illustrated on how to conduct such a campaign (including rules, though I probably won't use those). Almost all figures for this project are from the excellent Meso-American range by Chintoys - I might also add that these are some of the first figures I've ever collected that I intend to keep unpainted. Here are each of the protagonist's forces:
Spaniards - 4 x 6 man units of conquistadors, plus a few war dog handlers and their assorted mutts (dogs from a cheap toobs collection from Amazon (how appropriate!)
Portuguese - 3 x 8 man units - using the new Chintoys Spanish Warriors for these
French (!) - well, it could have happened...3 x 8 of Chintoys Italians (they look appropriately foppish)
All the Europeans can add to their forces from friendly (read, conquered) Indian types. As for the native kingdoms:
Aztecs - 6 x 8 man units
Maya - 8 x 8 man units
Mixtecs/Zapotecs - 7 x 8 man units
Cannibals (Tupi from Brazil, etc.) - 6 x 8 man units (using Iroquois by CTS for these)
Inca - 8 x 8 man units
As you can see, I've rather downgraded the Aztecs in terms of importance - I get a little tired of them - and will instead have the Maya and Inca as the two main power-brokers on the island of El Dorado; the Inca will have by far the most gold (the main motivator for the Europeans) but will be more remote, whilst the Maya will have a penchant for sacrificing any sods unlucky enough to be captured...
For rules I'll probably use tweaked Lion Rampant or The Sword and the Flame. All good fun and at the very least keeping me off the streets!