Former players who deserved a shot at a higher level

Trevor was brilliant but never quite seemed to have the mentality of a Top Player. I think the constant injuries he suffered in his formative years didn’t help.

There was talk of Sexton signing Gerry before he eventually went for Wilkins. That 75-76 QPR team was bloody good.

Yeah you're spot on with Trevor Francis, and we were linked with Gerry(my favourite non United player at the time along with Kevin Beattie), but think it was the right call looking elsewhere(Wilkins)as although they were both Cockneys, of the two Gerry would probably have struggled settling in the North more.

A fine player in his pomp driving the game from midfield though.
 
Weren't Man. United in for Senna one summer as a replacement for Roy Keane?

Yep, Summer 2006 - Fergie wanted Senna or Hargreaves having already signed Carrick. We made a bid for Senna on deadline day.

Riquelme played for Barca. Not many bigger clubs than that!

Oops, my bad Duffer.

In my defense, it was only a season and Barca were average back then. He was very good technically, definitely think he could’ve played a level above.
 
Maybe Forlan? Obviously didn't work out for him at Man. United. He tried but the fundamentals in his game like finishing and technique weren't really there.

Was brilliant at Villareal and Atletico Madrid although AM weren't the force they were now in his peak years there. Got a move to Inter but think he was 32 and was past his best as he peaked at WC 2010.
 
Did anyone mention Henrik Larsson yet? I know he played for Barca and United shortly, but he was already 32/33 when he moved to Spain and even older in the EPL. Spent his prime years at Glasgow despite being known as one of the best strikers around back then. I remember him having the highest rating of all players in 2002's FIFA WC game which was the first FIFA I ever played.

Maybe Pablo Aimar, too?

From current players, I'd say Marco Reus, Daniele de Rossi, Ever Banega come directly to mind.

In the Bundesliga, there have been quite a bunch of players who became actually "too good" for their respective teams but never tried their luck at bigger clubs although they weren't CL contender level. Exemplarily Raffael for Mönchengladbach, Marcelinho for Hertha and Micoud for Bremen in the 00 years, Max Kruse for Bremen/Wolfsburg/Gladbach, Kießling for Leverkusen, Hector for Cologne. You could also name Makaay for Bayern since he joined them in their weakest phase ever, not being anywhere European top quality.
 
Pre-2000 the game was different and the top clubs in countries like Turkey, Scotland or Romania would often have a star or more in their midst who would comfortably get into just about any club side in the world. And even the second-tier clubs in the big leagues had that sort of quality and competed for titles which meant there was little reason for Mauro Silva or Ruben Baraja to move anywhere. The game wasn't stratified as it is now and moving to a superclub wasn't necessarily a 'higher level'.

Aye, I tend to have mixed feelings when these topics arise as I miss the days when a player didn't necessarily have to sign for a Real or a Barca to be seen as one of the greats. The romantic in me loves players like Batistuta who spent the best part of their career establishing themselves as club legends and trying to drag a smaller club up a few levels rather than jumping ship to one of the elite at the first opportunity.

That said, Tugay was a great shout and I like @FootballHQ and @André Dominguez 's mentions of Forlan and Viduka too. Viduka had such a great skill set. Strong as an ox with a silky touch. Seemed a complicated character though. Lucas Radebe is another one from that Leeds team who could have moved upwards imo, although it's worth pointing out that Leeds were a young and highly promising team then.