The whole point of a try is to close that phase of play, let the defence regroup, let the fans have a leak or scratch their stones, and start again. With a kickoff at halfway.
Besides, conversions are not mandatory as it is - teams can elect to go straight to the kickoff. That they don't means the quick break - gathered thoughts, quick drink - is quite valuable in the game. Would rather see players get their act together with a quick break than see them get burned out because the fans think goal kicks are boring.
Besides, League has the balance between tries and place kicks right. AFL and Basketball have the same scoring method used ad nauseum throughout the game. Union relies on kicks too much. League rewards the skills of attack and defence AS WELL as the skills of ball control with hand and foot.
You're looking at about ~2min of game time lost when a goal kick is taken, this includes lining up a conversion then the kick-off. While it add moments of tension, I feel it does not constitute true "football" skills, but it is instead a very minor subset of skills that is awarded too heavily considering the effort and skill required to score a try in the first place i.e. it's much much more difficult to score a try than take a conversion. There is also a heavy element of luck involved. The winner should be the side that scores more tries than the opposition (that is if both sides concede the same amount of penalties). There would be no less tension imo if you only counted tries anyway look at soccer which only counts goals. Conversions kicks only give an inferior side a better chance of winning imo.