Not a frequent Delta flyer.
Tried to search the Delta forum, but could not find an answer.

PAID (no miles or upgrades) to fly KEF-MSP in Premium Select then MSP-HNL in Delta One.
Misconnected in MSP by 4 min so rerouted MSP-LAX in first then LAX-HNL in coach.
Arrived over 7 hrs late.

I have 2 questions:
1. What is an appropriate amount to ask for compensation for the downgraded segments (Delta One to first/coach) and 7 hr delay? A friend who is Diamond Medallion suggested asking for $2000 in travel credit (rt ticket cost $3000), but settling for $1500. With anger and emotion (most of the Delta people I asked for help were nice, but useless and one lady at the LAX Sky Club was offensive) I think $2000 is fair, but my rational side thinks I should request $1000.
2. What is the most successful way to request compensation w/ Delta? Phone? Online? I read on The Points Guy blog that it's best to ask in person > then social media > then phone > then online form. Everyone I spoke w/ at the airport (Sky Club and Help Desk) just referred me to the online form.

Thank you in advance for your advice.

Late arriving plane from JFK in KEF.
Not weather-related.

OK, so you paid $3000 for a round trip ticket and you want $2000 in travel credit for a delay and a downgrade on one segment of your outbound. With all due respect, your DM friend is either giving you poor advice or he/she is a customer that Delta may not really want if he/she routinely demands that type of compensation.

I expect any request in the four digit range is going to be viewed as excessive. I'd suggest asking for $750 based partly on the 7 hour delay (that's worth maybe $200 at most) and the rest based on flying in coach on LAX-HNL which is maybe about a 5 hour flight westbound. You might actually get that.

Stuff happens and I don't think you're going to get more than half of your ticket value back for a delay and a downgrade on one segment.

I'd call Customer Care at Delta. I've always had good results with them.

David

I don't have a lot of experience with Delta, but if you're asking for $2k, you'd probably have better luck going to some corporate department as opposed to the regular customer service channel.

What credit card did you use to book the ticket? Perhaps you can get some benefits from the credit card for the delay.

Doubt it, I don't see "emotional distress" anywhere in the post

For the delay yes - but wouldn't the downgrade compensations kick in as well?

Yes downgrade comp should apply as well regardless.

I would say that is a pretty significant downgrade from D1 equip to connection in domestic F and then Y with resultant delay of 7hrs.
Looking at flight history for DL 261 KEF-MSP, I'm guessing this occurred on Sat 6/2. Flight departed KEF over 6hrs late. Problems started several flights earlier with a 5hr late JFK-ATL-JFK route on Friday of which DL never recovered.

Lets face it, OP is not going to get $1000, unless the flight difference was actually that much from D1 to F/Y for MSP-HNL. However, definitely fare difference for the downgrade, plus the downgrade comp (what is that, $200+ for D1 to Y?) and something additional in form of goodwill for the significant delay and downgrade... but that part is likely to be in the form of miles.

Yes, so I would try the following if I were the OP. I'd call customer care, tell them my tale of woe, and then point out that I could file for $705 cash as the delayed flight originated in the EU and is plainly eligible.

I think then I would ask for $700 voucher in lieu of the cash, and $500 voucher as downgrade compensation.

I believe for domestic, the downgrade compensation is $200 (plus difference in fare). However, since OP was originally booked in D1 it may be higher.

This is separate from any additional comp for the disruption and late arrival.

I agree. OP should take into account that the voucher may reduce taxes, so could actually be better than cash, but no reason to tell that to the agent when you're asking for compensation.