Let's go with a 45000 Cr average for neutron stars, and 70000 Cr for Earth-like worlds. (Taken from
http://elite-dangerous.wikia.com/wiki/Explorer) This is without a first discovery bonus, of course.
For neutron field farming, let's go with an explorer having to travel 15000 ly to a neutron field, finding no first discoveries there (a rather pessimistic assumption) and once they're there, scanning eight neutron stars per ten systems visited. (One less for refueling from a scoopable star every ten jumps, and one less to account for any other travels they might have to do.) Also, let's go with two other pessimistic assumptions: that they never once get a first discovery bonus (unlikely) and that none of the NS systems they visit contain anything but the star. Which is of course extremely unlikely - this is just for simplicity's sake.
This also assumes that they find no ELW-s around any of the neutron stars, which is also highly unlikely.
For ELW hunting, let's go with an explorer finding one undiscovered ELW per 200 systems if they are randomly travelling (a bit optimistic assumption), then finding one every 100 systems when they are doing a targeted search. (The best examples I've seen are around 1 ELW every 75 systems.) Also, for simplicity's sake, let's say that an explorer has to travel 2500 ly to get to an area where all the ELW-s are undiscovered, so they get the first discovery bonus for all of them.
Let's go with an explorer having a 35 ly jump range, and being capable of making one jump per minute while travelling. While honking and jumping, they'd average 5000 Cr per system. (That would mean systems would have ten bodies on average.)
So, how do the numbers measure up then?
First part: there and back again
A1: the explorer needs to do 429 jumps to get to the neutron field. This will take them a bit over 7 hours, and they'll find two Earth-likes on the way, likely undiscovered. That means 2,355,000 Cr for the way there, and since it'll be a return trip, it's 14.5 hours and 4,710,000 Cr. That means they make ~325,000 Cr per hour in this part.
B1: the explorer needs to do 72 jumps to get to the "ELW field". This will take them 1.2 hours, and they're unlikely to find an Earth-like along the way. The honk-and-jumping nets them 360,000 Cr. Assuming an exact same trip back again, it's 2.4 hours and 720,000 Cr for the return trip. That means they make 300,000 Cr per hour in this part - roughly the same amount they'd make if they went for the neutron fields instead, but with a lot less time investment.
Second part: farming NS-es / hunting ELW-s
A2: once they're there, the explorer finds 80 NS-es per 100 systems visited, netting them 3,600,000 Cr. The other twenty systems would net 5000 Cr each, so the total per 100 systems: 3,700,000 Cr. Let's go with a pessimistic assumption of the explorer spending three minutes in each system, as they still check the system map and pick the next destination from the galaxy map: that means they'll need five hours. Which means they'll make 740,000 Cr per hour in this part.
B2: for simplicity's sake, let's say that an explorer spends three minutes in each system while looking for ELW-s as well. (This includes looking at the galaxy map and flying to the one ELW they'll discover.) In this case, as they'll find one ELW per 100 systems, they'd get 105,000 Cr for the Earth-like and 495,000 Cr for the other systems. That means they make 600,000 Cr per five hours, so it's an astonishing 120,000 Cr per hour.
But hey, let's be a bit optimistic and assume that for every ELW, an explore would also find four WWTC-s that are worth the same amount. In effect, this could mean they'd find five Earth-likes per 100 systems. In that case, the total would be 1,000,000 Cr, bringing it up to 200,000 Cr per hour.
Total time and credits:
Let's assume that both explorers spend twenty hours with their searches.
For the NS farming, that'll mean 14.5 hours of travelling, netting them 4,710,000 Cr, then 5.5 hours in the field, netting them 4,070,000 Cr. The total is 8,780,000 Cr. On average, this would be 439,000 Cr per hour.
For the ELW hunting, that'll mean 2.4 hours of travelling and 17.6 hours of searching. If we go with the more optimistic rate of 200,000 Cr per hour on the latter part, the total profits for the twenty hours would be 4,240,000 Cr. On average, this would be 212,000 Cr per hour.
Which is less than what they'd earn if they just honked and jumped the whole time.
So, what would be needed to bring ELW hunting up to NS farming? Again going with the optimistic assumption that they'd find effectively five ELW-s worth of scans for 100 systems, the increase in ELW value would also compensate the NS farmers a bit while they are travelling. So, let's just compare the second parts first. For an ELW hunter to make 3,700,000 Cr per five hours, instead of the base 70,000 Cr price,
Earth-likes would have to be worth 430,000 Cr. (Without the FD bonus.) That's a
6.14x multiplier. Since that included four terraforming candidate water worlds, they'd have to be multiplied the same too.
And this is assuming that no Earth-likes will be found while farming neutron stars. I haven't farmed neutron stars, so I have no idea how many you'd need to visit on average to find one ELW.
Finally, as I already mentioned in the tl;dr summary, even in this dreamlike scenario, exploration would still yield considerably less credits per hour than almost every other activity in the game. If you want to see something funny, try calculating how much the multiplier would have to be to match long-distance ("Robigo") smuggling runs.
Of course, said runs involve much more risk, and the profits from them are far higher than anything else in the game anyway. For the record, I'm in no way saying that exploration should match that.
If you've actually read this wall of text, thanks for taking the time to do so!
