Using special yeasts instead of those included in the kit (even "top lines" like Muntons Premium Gold or John Bull Master Class) can I reach a different and a considerable result? Worth it?
Specialty yeasts are good for beers that require a specific flavor profile from the yeast, like Hefeweizen or a Lambic. For beers such as an IPA where the hop flavor is dominant a clean fermenting dry yeast will not only give a the hops room on your palate but are also cheaper.
Personally I tend to stick with Safale US-05 for most of my beers.