It's really hard not being a native speaker, but i'll give it a go.
With プッツン来て爆走よ, it's probably easier if you can provide the sentence before it? Because without context I think it could just be the guy grumbling about the lack of help. 爆走 could really just be him wanting to expel his frustration (roar? perhaps - google translate seem to agree with me there).
My understanding is this sentence is those ー really is う to emphasis the annoyedness of the person speaking - what you have there is fine.
なんつって… given the person was praising Colosseum with katakana emphasis 最適ィ in the previous sentence, my take on the 3 sentences is something like the following:
だからいっぱいデジモンと会いたい！ lots of Digimon you can meet!
それにはコロシアムが最適ィ！ Colosseum is the most awesome (place?) (emphasis on awesome)
なんつって… just kidding
コロシアムにきたのはいーけど！ but Colosseum is still good spot (to find Digimon?)
Basically she (?) is trying to play down the 2 line made as a joke (冗談で言って) - and the 4th line is the proper explanation (弁解する語)
Again don't take my translations to your work as I have no context of Digimon at all, but hopefully you get the idea on the translation meaning.
Actually that bit about the Colosseum now totally makes sense in the concept of the story! She wants to put emphasis on the fact, that for THEM the colosseum is the best place (because they are ranked no 1 there) but they don't want us to know, so she plays down the fact, that they actually frequent the Colosseum and are ranked Nr.1 There. Wow, it was staing at me the whole time.
The sentences before that problematic one are like this:
あの子、いっぱいのデジモンみて\nキャッキャなりすぎて… But when that kid saw all the Digimon here she got totally excited.
ぶっとんでっちゃったの！\n文字どーり！ She freaked out. Literally.
どういうこと？ What do you mean?
I think you might be right about the grumbling about the lack of help, but how to translate it in a feasible sense?