I disagree. Portugal had a huge chance of becoming a power once again with Pombal's reforms. It wasn't quite enough in OTL but, if you're interested, check out Lusitania's timeline "The rebirth of an empire", and you'll see what I mean.
Honestly though, just jave them use the brazillian gold to fund internal development of manufactories like the french. Maybe you could have them snatch some territories in the War of Spanish Succession. Even better, make them reconquer all possessions lost to the dutch. Portuguese australia os possible too.
See signature that is all you need. As pentapolim stated during Pombal tenure Portugal got a good start. We just gave it some gusto and made sure his reforms stick.