IFR conditions is any condition in which you have to comply wth the rules for instrument flight. Whether it's weather or being in the flight levels etc. To me that's carrying proper fuel reserves.
If you use the definitions of the phrases used in the FAR's, it would appear that as long as the flight is going to be conducted in VFR CONDITIONS, 30 mins of fuel is required, regardless of if you are on an IFR plan or not.
If there is an FAA interpretation of this stating otherwise please post it. But the FAA is very deliberate in the words and phrases they use when writing a FAR. By using the word "conditions", they mean just that, the conditions, not rules, the flight will be conducted in. Even using the word in, instead of under, as in rules the flight is conducted under, seems to me, to say they are talking about actual weather conditions and not flight rules.
That is my take which is worth absolutely nothing.
All taken from the current FAR's
IFR conditions means weather conditions below the minimum for flight under visual flight rules.
§ 91.151 Fuel requirements for flight in VFR conditions.
(a) No person may begin a flight in an airplane under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed—
(1) During the day, to fly after that for at least 30 minutes; or
(2) At night, to fly after that for at least 45 minutes.
(b) No person may begin a flight in a rotorcraft under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed, to fly after that for at least 20 minutes.
§ 91.167 Fuel requirements for flight in IFR conditions.
(a) No person may operate a civil aircraft in IFR conditions unless it carries enough fuel (considering weather reports and forecasts and weather conditions) to—
(1) Complete the flight to the first airport of intended landing;
(2) Except as provided in paragraph (b) of this section, fly from that airport to the alternate airport; and
(3) Fly after that for 45 minutes at normal cruising speed or, for helicopters, fly after that for 30 minutes at normal cruising speed.
(b) Paragraph (a)(2) of this section does not apply if:
(1) Part 97 of this chapter prescribes a standard instrument approach procedure to, or a special instrument approach procedure has been issued by the Administrator to the operator for, the first airport of intended landing; and
(2) Appropriate weather reports or weather forecasts, or a combination of them, indicate the following:
(i) For aircraft other than helicopters. For at least 1 hour before and for 1 hour after the estimated time of arrival, the ceiling will be at least 2,000 feet above the airport elevation and the visibility will be at least 3 statute miles.