Whether or not Spike Earring's cost is worth it depends on what your alternatives are. You have to ask yourself certain questions.
What is the rest of your gear like? I'm guessing if you can't afford Spike Earrings, you can't afford a good accuracy set for TP. If your gear doesn't have enough accuracy to hit about 80% sans food/buffs, you are likely better off using Sole Sushi. If you can't afford that, even Crab Sushi will work. You should be worried about Sniper rings, Minuet Earring, and try to party with a BRD! Acc food + minuet/march from BRD is better than attack food + madrigal(s).
You also have to worry about what your other endgame ear options are. Do you have a DM earring? Is it Suppa? What about Apoc Nigh? Did you pick a 'mage' earring from either? Do you have Brutal yet? None of these are even available until 72+, but if you don't have, or don't plan on getting, at least one of either Suppa or Hollow (or for some reason Ethereal), then Spike Earring is a good investment. It's either that or the even more expensive Merman's Earring.
So it really comes down to 2x Spike or Spike/Minuet (if you have a BRD), at least until you can equip (or get) some of the endgame earrings. I haven't leveled in a long time, but I'm pretty sure that those are still your best options. Once you have enough gil saved up you can sell your earrings/rings to buy 2x Snipers, then get by on NQ earrings until you can save up enough gil again. That's assuming your other slots are ok already... if you need a Scorpion Harness, by all means get that first.
And your farming issue. You have RDM and BLM both at 75. If you have access to Sky and ENMs, you shouldn't have any problems making gil. Aside from obvious solo and low-man enterprises, I'd say you are missing out on two very good gil makers - ISNM Shadows of the Mind, and KSNM30 Royale Ramble. I think ISNM is probably one of the easiest ways to make gil in the game right now, as all it takes is meriting/Besieged + some volunteers. Royale Ramble is also good because of the 100% drop of an Orichalcum Ingot (~300k depending on server), and the chance at a couple other 200k+ drops. The fight is a little more difficult, and access to it is more limited, but again, easy money. Hint - farm Beastemen and Kindred seals in one of the starter Promyvion zones. You can double it up with the NPC earring recharge, get Alchemy mats for AH, and even set yourself to merits if you want.
You could also try getting people involved in ANNM fights. The only requirements for trying them are access to the past and Allied notes, so this one is good if you do a lot of Campaign. Some of the fights are more difficult than others, but they each have a variety of rewards. The gil drops can be extremely nice, too... my first one netted our group (6 people) a Star Sapphire from one area and two Khroma Ores from another. We ended up getting 460k each for about an hour and a half of fighting and travel. One guy even got a nice Demon Helm with +macc on it.
Anyways, the point is that there are plenty of ways to make gil that don't involve what people normally think of as farming. You shouldn't be farming for gil, so much as farming for ways to make better gil. Spend two hours killing bees for 10-30k worth of drops, or spend 2 hours getting exp and a chance at several million gil? Where's the fun in fighting bees, anyways?
BG elitists <3 haste.
Allatards/uber casuals hate elitists.
Allatards/uber casuals hate haste, as valuing it would acknowledge that elitists are right
People don't hate emo kids because they're "misunderstood." People hate emo kids because they're useless.
PUP is an average to above average DD... when not in a zerg situation... or on particularly hard targets... and when properly configured... on windsday... with a RDM...