I have never ever seen a digital OG Xbox game discounted on the Xbox Marketplace. Can anyone attest to this? I find it strange since Sony discounts its digital PS1 and PS2 games more than not.
Original Xbox Games have only been on the marketplace a few months to be fair, in comparison Sony has been selling PS1 games since the PSP days. That said digital games on the Xbox are always massively over priced, even when they have 50% off sales you can often still purchase the game cheaper on disc here in the UK. Its the reason i still purchase games on disc where possible. I'm not sure how the prices of used original Xbox games on disc compare to digital downloads these days, however it might be worth having a look on Ebay / Amazon to see if you can get any good deals. That reminds me i've hard Conker: Live & Reloaded is now backwards compatible, I should give that as its the first game I own on disc that's backwards compatible.
Even before the XB1, OG Xbox games were sold digitally so they could be played on the 360. Even then I do not remember a single instance where they've been discounted, staying at $9.99 USD (except for Red Faction 2, which bewilderingly cost $14.99 USD, unlike virtually every other OGX game).
Ah yes i'd forgotten the 360 got a few downloadable Xbox Classic games. They never really pushed it, of the 31 games released the last was almost 10 years ago. I suspect they had long since been forgotten about. Its a shame really as games like Halo 2 did play really well on the Xbox 360. Lets hope these keep getting pushed on the Xbox One, if they do i'm sure some sales will happen sooner or later. I'd personally look for games on disc though, you can probably get some pretty good deals.
I'd prefer to buy them digitally for when I get an Xbox One, even if I have the physical copies. That way the aging discs are never damaged by a faulty system, and always work as flawlessly as they can. Also buying the digital ones will show companies that there is an interest and more enhanced OG Xbox games will appear. I don't think they are counting on everyone playing them for free on discs. The new lineup this month is killer.