To read Eliot’s The Wasteland and understand all the allusions, including the unintentional ones, would take a lot of cross-referencing, and these days, a lot of googling. However, I don’t find I need to understand every reference to enjoy it. The poem can be appreciated, and mainly understood, without months of in-depth study (not that I’m knocking anyone who has undertaken such a study. I just haven’t the time).
However, I have read a few poems recently in which poets have slipped in obscure references, and without some understanding of the references, the poems didn’t make much sense. It’s as if these poets have felt the need to prove themselves superior to the hapless reader. Even worse when they add as a footnote, “Krysyck’s lines only have a faint echo in this poem,” as if the reader is supposed to know exactly which Krysyck poem(s) is (are) referred to (and even whether Krysyck is a poet, novelist, historian, film director, or what).
I find the approach intellectually dishonest. I could easily take a trip to a musty library, dig out some facts that few people are likely to know, and write a poem to expose its readers' ignorance. Of course, any of these readers could do the same to me.
On the other hand, there must be ways of writing on subjects that aren’t familiar to many people without packing the poem with so much background information that the poem looks like an encyclopaedia entry. As a reader, I’d be prepared to do some work to understand a poem if I think the writer is doing some work to communicate his/her obscurities, so maybe there is a balance there somewhere. But not an easy balance to find.
Later edit: I’m editing this in because there might be a part-answer in George Szirtes’ entry of 9.3.06 titled The Waste Land.
Especially this paragraph:
“I try to explain how the poem rang in my head without anything as clear or definable as a meaning, that I knew little about de Nerval or Webster but felt the dramatic core of the poem as power, because a poem is a piece of writing that requires nothing external to complete it, since the external can only adumbrate, amplify, enrich but never complete a poem, so the worst thing you can do with The Waste Land at the beginning is to clobber yourself with learning and solving, because it is not a crossword puzzle to be solved or a peculiar rare parchment to be stored away in a sealed cabinet at the right temperature and humidity, but a world created in a state of breakdown, one you walk into, dizzy and staring and haunted.”
A poet who writes only a crossword puzzle to be solved isn’t going to leave a reader “dizzy, staring and haunted.” But The Waste Land stands up on its own as an enormously affecting work, even if one misses all the allusions and influences.