Each pair had a larger than life character who was, by any indication, the more talented and beloved figure of the two. Aside from physical similarities, each pair had a stranglehold on their respective industries for a small yet unforgettable window in the early to mid-90s.
Spade and Farley were part of "The Bad Boys Of SNL" and helped make the show hip again, and starred in one of the great comedies of the 90s, Tommy Boy. Meanwhile, under the "Bad Boy" record label, Diddy and Biggie collaborated on Ready to Die to put East Coast rap back on the map after years of West Coast domination. 

Unfortunately, the lives of both Farley and Smalls were tragically cut short in 1997 from entirely preventable incidents. Both Spade and Diddy have soldiered on, but today represent mere caricatures of their former selves, and the question of "what if?" still lingers.

The credibility and star power of both Dane Cook and 50 Cent has dimmed considerably over the last couple of years, and each has endured their share of criticisms from fellow performers, from Ja Rule to Joe Rogan. That's only the beginning of the similarities, though.
Both Cook and 50 released their breakthrough albums in 2003, with the titles of both dealing with bodily harm (Get Rich or Die Tryin' and Harmful If Swallowed).
Two years later, they each cemented their status as the most commercially appealing artists in their field with the release of massive and record-breaking albums with titles that alluded to physical harm to others (The Massacre and Retaliation.) In that same year, both appeared on floundering comedy institutions, Cook hosted SNL and 50 lent his voice to The Simpsons.
Since then, they've each gone on to appear in generally unwatchable movies (Home Of The Brave, Righteous Kill, Employee of the Month, Good Luck Chuck, etc.) and unwatchable television shows that bore their name ("50 Cent: The Money And ThePower", and "Dane Cook's Tourgasm".) The popularity of each has diminished thanks in large part to the rise of two artists, Kanye West and Zach Galifianakis, who offer a different artistic style and who collaborated to make this video.

Aside from directly influencing every great comedian and musician of the past 30+ years, possessing must-read memoirs, and being the ultimate "drifters", Steve Martin and Bob Dylan have similar career paths and cultural influence. Both started out political, as Dylan gave the world some of its greatest protest songs, and Martin worked as a writer on the politically charged "Smothers Brothers Comedy Hour."
Generally speaking, there is no middle ground for appreciating Martin and Dylan: when it comes to the ironic surrealism of "Grandmother's Song" or "Desolation Row", you either get it, and fall in love, or you don't.
At the height of their popularity, with Dylan's folk and Martin's stand-up, they were phenomenons, yet they shocked everyone by walking away to explore different avenues, and what resulted were the groundbreaking and astoundingly brilliant Highway 61 Revisited and The Jerk.
Since then they've branched out to different things, Dylan made Gospel records, Martin focused on writing, and though they don't necessarily have the cultural impact today that they once had, Martin's New Yorker humor pieces, plays, and recent guest spot on 30 Rock, and Dylan's last two critically-acclaimed albums and never-ending tour have proven that they are still viable and relevant artists to this day.

Each backed by a pop culture titan, Ron Howard and Andy Warhol, the seasons of Arrested Development and albums of The Velvet Underground, especially the first 2, are widely regarded by critics and fellow artists alike as some of the most influential and greatest in history, despite their lack of widespread commercial appeal. Each showcased style and writing which directly challenged the conventional process of their mediums and offered a striking alternative to what was being produced at the time.
"The Velvet Underground & Nico" was released in 1967 during "The Summer of Love", in which every successful band wrote lyrics about love and peace and using drugs to free one's mind, all while accompanied by a harmonious and uplifting musical backdrop. Meanwhile, Lou Reed's lyrics dealt with greed, nihilism, and using drugs to dull one's pain, and were accompanied by dark, fuzzy, and droned out guitars and violas. Conversely, Arrested Development entered a sitcom world filled with identifiable, likable, family-friendly characters with obvious, carefully set-up jokes set to laugh tracks, and proceeded to show a world filled with greedy and nihilistic characters with almost imperceptible and laughtrack-less jokes.

Time will tell, but one can assume that the influence of Arrested Development by way of inspired comedians and writers will be felt and seen in the coming decades similar to the way it has for bands inspired by The Velvet Underground.

Ironically, while the fan base of each is comprised primarily God-fearing people, the body of work they've managed to produce is as clear an indication as any that God does not exist, and yet through this they've managed to make more money than Him.