hmmmm....firstly i am going to absolutely disagree with our friend Green. Sorry Green. While it is indeed important not to "over clean" anything it must also be understood that keris blades are meant to be maintained with regular cleanings. So i would recommend that you either attend to this yourself or send it out to a professional for attention. As the current custodian of this keris it might even be seen as your responsibility.
Firstly, the surface texture that Green suggests you maintain here is
not original to the blade. Keris blades all start out smooth. The topographic surface of a keris like this has developed over what has probably been at least a century of regular acid washings and blade staining with warangan (arsenic and lime juice). I'm not necessarily suggesting that you acid wash and stain this blade yourself. In fact, if this were in my hands i probably would not re-stain this blade even though i do have experience with the process. However, there are a number of things i absolutely would do. It would be much easier to give this blade the TLC that it needs if you detach the hilt from the blade. If there is movement in the hilt this should be very easy.
Gently wiggle the handle back and forth while steadily attempting to pull it off the tang (pesi). I say
gently with emphasis because your ivory hilt already has some damage and you do not want to crack it further.
Once the hilt is free you will probably find that the tang has a wrap of some kind of material around it to keep the hilt firmly in place. I would guess that there is a little bit too much of that material in place since the crack on your hilt seems to be opening due to the pressure. When you reassemble the pieces after cleaning i would wrap this with slightly less material so that the hilt crack does not bulge. It is better that there is a little movement in the hilt than for you to crack it further to keep it tight.
I would spray the blade complete down with WD-40 and go at it with a hard tooth brush. Let the WD-40 sit for a while first to help loosen the rust. This should not remove the darkened color from the warangan much at all. As for patina, while that is perhaps important for wooden parts (which i would oil btw) it is not the tradition for a well kept keris blade. As i stated, traditionally a blade would be regularly cleaned in an acid bath and re-stained. So what many deem as patina doesn't really accumulate on keris blades. You might also then work on some of the tougher rust areas with a metal needle and a magnifying glass. This would be especially helpful in the separation area where the gonjo meets the blade.
I would also use a polishing cloth on the brass pendok (no pastes or other cleaners though). This type of open pendok may well of had a piece of velvet material in the stem (black or red might look nice to me). Keep in mind that keris are part of a living tradition and are meant, among other things, to be an article of formal dress. They should not look like dingy artifacts of a dead culture. They should have sense of dignity about them.
I would follow through on Detlef's instructions for care of the ivory hilt. They get thirsty over time. When you reassemble the keristake care not to wrap the tang too much that the crack re-opens in the hilt.
As for "ugly", that is indeed an eye of the beholder kind of thing i suppose. If you still feel the same way about this blade after sprucing it up let me know and i will gladly take it off your hands.