I have 30K km on odo too. I used 0w20 from Honda showroom. Will go with 5w30 next time.
Try checking your gear oil level (near passenger side wheel) before going for cat con cleaning or spark plugs as most forums suggest. Also get the AC cabin filter replaced (under dashboard glove). See if this helps.
And try to check avg without AC in night time. It could be that during day time even though u have 26 C on auto AC but outside temperature being 40 C makes the AC work at 20 C or less to maintain cooling. That's why ur not getting better avg.
Just saying don't jump into tuning and stuff unless its needed.