I think Mashima should just tweak his characters a bit to make them more appealing. You can't change the whole manga into a "every fight is solved a clever way" (say Rurouni Kenshin for example), it wouldn't be Fairy Tail anymore, someone has to bring the "nakama" thing sometimes, and I think it's the place of Natsu.
But at the same time I have the feeling that it would be very cool to define once and for all the way the characters fight. My opinion :
Erza - she is more like Laxus or Gildartz, she's about brute force, though she is able to find her opponents weakness very quickly (say Midnight fight) . I think it wouldn't be bad to have her go berserk more often in the end of the fights and destroy everything and terrorize her opponents to the point they shit on themselves
Gray - Gray has some good fights (Ultear/Rufus), he is about tricking his foes and setting traps. gray should never be in frontline but always trying to trick people and make them do what he wants and stand where he wants them to stand.
Lucy - Lucy's magic has an important cost and she is a character intended to make people laugh like Happy, she's kinda weak, but promising. In think either she should be used to win time by only using one spirit and making her opponents chase her till she finds an ally, or her fights should always be short, like ... throwing everything she's got the most efficient way at the end of the battle of one of her friends to reverse the situation, deplete her magic with urano metreia and KABOOM!
Natsu - Natsu is about nakama. fuck ... fuck ... well let's say natsu is tough, he can sustain a lot of damage and never give up. he's not clever and never will be, it would not be him. but he understand fire and can find ways to use it at his advantage against his foes.
Wendy - easy, she has the supporting role. I think she could be used to reset fights. Just blow everybody away with wind and let's start again ok?
MOST IMPORTANTLY ... WHY ARE THEY A TEAM OF 4 IF IT IS TO FIGHT ALONE ALL THE TIME?
Please Mashima ... it would be 10 time more interesting to have fights where you show how they could combine their skills to defeat their opponents ... there could be tons of possibilities ...