First, why? Adding some amazing feature only available in spark?
Maybe lazy, maybe smart, it's all argumentative. :).
Unless I need to, I personally tend to not upgrade. Seen it's not a security issue and it works why bother. I have clients still running l3 with out an issue.
FYI, you don't need to remove auto increment, you can explicitly set it. Obviously it need to be unique, but you can set it like any column. Also you can export from sql in a variety of formats and reseed a new db with a few clicks or commands.
Why? The framework has gone through many changes since 4.2, and I've also become a bit better with the tools. I think I'd like to recreate what I have, make it better...
I can tell you that you will have tremendous difficulty porting a 4.2 app to Spark. If even thinking about it, forget it. If necessary, plan on rebuilding the app based on Laravel 5.3. The problem is that Spark is heavily opinionated and really difficult to attempt to modify. Add on sure, modifying opens up a vicious cycle of technical debt. It would take far less time to rebuild it using Spark. The main purpose for Spark is subscription management with only free, monthly and yearly provisions. Everything else must be done through Cashier...which Spark is built on. Other than that, you build any laravel 5.3 site around it.
