Isn't that exactly what a Wizards spellbook is?
Is this what you are saying the Trinket Mage does? IS there an endless casting and recasting of the spells available each day? Like a Sorcerer who's spell selection is limited by how much money he spends on acquiring and upgrading the strength of his spell selection? Is it a like a Warlock who can cherry pick his invocations off the Sorcerer/Wizard list by spending more money and crafting time?
Because if this is what you are saying the Trinket Mage does, then I could see it being cool. Limiting the variety of spells available by making you have to work and pay for them, but casting an unlimited amount of times per day. Run the risk of your trinkets being lost, stolen or sundered.
I'd play that.
Now, if you're spell selectioin is limited by how much money and time you invest, and you run the risk of your Trinkets being lost, stolen or sundered, without any advantagious return from the class that would make me want to play it over a different class, then I'd have no reason to play a Trinket Mage.