The story about Guimerà is far from being clear, some simply say it's not true. What's outstanding to me is the fact that he was proposed for seventeen consecutive years. But then, Kadare was also nominated for fifteen years.
Guimerà was certainly the most famous Catalan playwright at the time, even beyond Catalonia or Spain. His play Terra Baixa opened in Broadway in 1903 and it was filmed as Marta of the Lowlands by Searle Dawley for Paramount in 1914. Leni Riefenstahl adapted it in Germany as Tiefland in 1954, several operas were made and it has continued to have versions and translations through the years. Manelic, the main character alongside Marta, is probably one of the archetypes in Catalan literature. Funnily, the 1904 Nobel Prize Echegaray was his translator into Spanish.
Several suggestions of Catalan authors for candidates took place along the century (Josep Carner, Pere Calders, etc), but often with problems or lack of agreement. A high consensus was reached for Salvador Espriu. (Selections of his poems have been translated into English, as well as his Ariadne in the Grotesque Labyrinth, a book of narrations in different techniques) One of the Swedish academicians, Artur Lundkvist, interviewed about him in 1976, said: 'I don't really think Espriu has any chances for the Nobel. It is of interest only to Catalans, not universal. And I say the same about Foix, Joan Oliver and Josep Pla. I can only say that Porcel is quite promising.' (Note: I'm retranslating, not quoting the actual words) Harold Bloom, though, included Espriu among his list of Catalan writers in his book of the Western Canon, and declared in 2002 that he should have won the Nobel. Regarding Lundkvist's reference to the Majorcan Baltasar Porcel, mostly known in English by his Horses Into the Night (Cavalls cap a la fosca, 1975), some do think indeed that, had most of his works been in Spanish, he'd have certainly won the Nobel.
There's also the context of the beginnings of the 20th century, when there were still attempts of a cultural brotherhood between Catalan and Occitan, two literatures with a glorious medieval past but that had experienced a dramatic decline in the Early Modern centuries. However, while very close, the languages are not the same, nor is the number of speakers. Catalan literature recovered its prestige during the 20th century and is nowadays a vibrant middle-sized European one, with books being translated to several languages, while Occitan literature is that of a minority.
But for now, Catalan, alongside Ukrainian, Romanian, Dutch and Bulgarian, continue to be in the European waiting room.