I set goals for myself. If I, say, set for myself the goal of creating at least one character of every class combination, even if I don’t necessarily enjoy every single second of the process of getting those characters levelled and geared up, I find satisfaction in achieving the end goal and enjoy specific milestones along the way. I always set my sights on the nearest goal ahead of me and work towards that. So even if the micro-aspect of the second-to-second gameplay isn’t challenging me at the moment, the proximity to the nearest goal keeps driving me forward.
The way I play I usually reach lvl 100 in early Ultimate (if I do Elite) or mid-to-late Ultimate (if I skip Elite, which I’ve started doing only now, after 4.3k hours of play, because Elite is a real low-point for GD). So my “xp drought” stretch isn’t nearly as long as yours was, which certainly helps keep me engaged.
I also stipulated that no character is allowed to have illusions until they reach lvl 100. So I may have an aesthetic vision for a character in mind and I just have to sit on it and wait, and let the excitement build up. And then when I reach lvl 100 I get to get all that energy out and tinker with the illusionist for like an hour to get the look just right.
In order for a character to truly complete the game, they also have to max out every reputation, beat every available nemesis (as practice and a testing ground for how the character will do in SR) and do all the secret quests (except Crate of Entertainment, cause fuck that fight, never beat it and probably never will given the time required for resetting after every death).
And then, once the character is done with the campaign, they have the task of doing SR75-80 within timer with reliability. That sometimes involves some major changes to gear or devotions so that’s another thing that keeps me engaged. I’ve seen how the character does against a wide variety of content in MC, now can I make it work at high SR or will I have to compromise my idea for the build to make it more viable?
And once I’ve beaten that, the character retires, and I only play them if I feel like it or I have an idea how to improve them further (while sticking to the flavour/vision for the character as much as possible), or if there were balance changes that revolutionise the build somehow. Because I end the playthrough with the overcoming of very difficult content with MY custom build (I never use guides, which is funny cause I used to write them for D2), usually culminating in a final, tense boss fight at SR80, I end the character with a high point. The playthrough doesn’t just peter out until I don’t feel like playing, it ends in an adrenaline rush (well, at least in cases where the character feels in danger at SR80). That keeps me excited to pick up another character and go through that again, so that I can see if my next crazy idea ends in a similarly euphoric victory.
With almost every ARPG, repetition will set in at some point, you stop finding new things and drastically improving your build from area to area. So I think being goal-oriented really helps keep you going after the good stuff. And if the game sets goals that are too far apart for you (beating campaign on Ultimate, etc.), you create smaller goals to complete for yourself along the way.
But all of that hinges on you enjoying the game, of course. Adding extra sub-goals into a game or genre that doesn’t really excite you only introduces a layer of tedium on top of the repetition.
) and to remove any covered area on the map (it irritates me if I see those smoke layers 
) Then I go ready few sets of gears (as close to the desired ones as possible from the smiths if it is craft-able) and different augments to fight the celestials .
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great job mate !