The additions in the Ring-maker cycle really breathed new life into the Secrecy archetype and the Ithilien Lookout is a very clear example of that. For one thing, it's the Secrecy cost-reduction done right - it's a good deal when discounted, but still palatable (if a little overpriced) if you happen to have left Secrecy. 2 resources for 2 and 1 for a useful enters play ability is still alright in the right context (and played in a Gondor deck his stats get better, increasing the value), and at 1 it's a steal. Much better than some of the earlier Secrecy cards which were more or less unusable outside of Secrecy.
The other aspect is that the ability really ties into how a lot of Secrecy decks like to work. The usual modus operandi of a Secrecy deck is to use its low threat to get some breathing room from the encounter deck while it amasses power and takes control of the board. so for starters the ability to scry the top card of the encounter deck directly ties into a strategy built around taking tight control of the game, and indeed into gradually taking control in a slow build-up, since it allows for more informed questing and thus more efficient general application of your available power, which in turn can make it easier to amass more power. More specifically though, the breathing room such a deck gains will often take the form of not needing to engage enemies. But leaving those enemies in the staging area can lead to an uncomfortable build-up of threat (whereas treacheries can be cancelled or otherwise dealt with and locations can be explored), and Secrecy decks tend to have less good options for potentially engaging and killing enemies than for simply acquiring high . The Lookout is thus a twofold boon to such decks, in that he provides cheap to kill what enemies do appear more easily, and he also allows you to potentially discard an enemy you can't deal with from the top of the encounter deck before it enters play, thus providing potentially very significant bolstering to what was otherwise something of a potential weakness in the archetype.
Overall, a very worthy consideration for any Secrecy deck using the sphere, and potentially also for some Gondor decks, or just decks built particularly around encounter deck manipulation. Certainly not a universally applicable card, but very useful to his particular archetypes.