The phrase "gain enthusiasm" is correct and it is usable in written English.
You can use it when you want to talk about becoming more interested in something or developing more enthusiasm for something. For example, "I was struggling with my work until I found ways to gain enthusiasm for the project".
Gaining enthusiasm, hundreds of AK's and RPG's and every other kind of terrifying tool become props in this dance and they shake and stir in ways that seem to be from a long forgotten era.
Fund-raisers attributed the six-month gains to enthusiasm among Republicans about controlling the White House after an eight-year absence.
Based on the possibility of cellular neuroprotection and early preclinical results, stem cells have gained widespread enthusiasm as a potential treatment strategy.
But in three years, Robert Glover has introduced the Chinese to the idea of fostering, helped them set up a pilot project in Shanghai and gained their enthusiasm to extend the idea across the whole of the country.
Performance of economic analyses in association with randomized, controlled trials (RCT) has gained increasing enthusiasm in recent years.
"In America, he has gained fresh enthusiasm in a new situation and he looks very, very well," said the Republic boss.
While the margins produced by these and other surveys vary, they collectively point to a consistent underlying trend: Big gains in enthusiasm among Democratic partisans have helped boost Obama since the party conventions.
For example, perceived "gains for enthusiasm for biology" due to Biological Inquiry are lower (average 3.21 ± 0.09 SE) compared with Zoology (3.76 ± 0.12 SE).
The power utilities hope to gain from the enthusiasm for plug-in electric cars, which could spell trouble for the oil companies.
